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Chapter 10. Authorization in dCache

To limit access to data, dCache comes with an authentication and authorization interface called gPlazma2. gPlazma is an acronym for Grid-aware PLuggable AuthorZation Management. Earlier versions of dCache worked with gPlazma1 which has now been completely removed from dCache. So if you are upgrading, you have to reconfigure gPlazma if you used gPlazma1 until now.


Though it is possible to allow anonymous access to dCache it is usually desirable to authenticate users. The user then has to connect to one of the different doors (e.g., GridFTP door, dCap door) and login with credentials that prove his identity. In Grid-World these credentials are very often X.509 certificates, but dCache also supports other methods like username/password and kerberos authentication.

The door collects the credential information from the user and sends a login request to the configured authorization service (i.e., gPlazma) Within gPlazma the configured plug-ins try to verify the users identity and determine his access rights. From this a response is created that is then sent back to the door and added to the entity representing the user in dCache. This entity is called subject. While for authentication usually more global services (e.g., ARGUS) may be used, the mapping to site specific UIDs has to be configured on a per site basis.


gPlazma2 is configured by the PAM-style configuration file /etc/dcache/gplazma.conf. Each line of the file is either a comment (i.e., starts with #, is empty, or defines a plugin. Plugin defining lines start with the plugin stack type (one of auth, map, account, session identity), followed by a PAM-style modifier (one of optional, sufficient, required, requisite), the plugin name and an optional list of key-value pairs of parameters. During the login process they will be executed in the order auth, map, account and session. The identity plugins are not used during login, but later on to map from UID+GID back to user names (e.g., for NFS). Within these groups they are used in the order they are specified.

auth|map|account|session|identity optional|required|requisite|sufficient plug-in ["key=value" ...]

A complete configuration file will look something like this:


# Some comment
auth    optional  x509
auth    optional  voms
map     requisite vorolemap
map     requisite authzdb authzdb=/etc/grid-security/authzdb
session requisite authzdb

auth auth-plug-ins are used to read the users public and private credentials and ask some authority, if those are valid for accessing the system.

map map-plug-ins map the user information obtained in the auth step to UID and GIDs. This may also be done in several steps (e.g., the vorolemap plug-in maps the users DN+FQAN to a username which is then mapped to UID/GIDs by the authzdb plug-in.

account account-plug-ins verify the validity of a possibly mapped identity of the user and may reject the login depending on information gathered within the map step.

session session plug-ins usually enrich the session with additional attributes like the user’s home directory.

identity identity plug-ins are responsible for mapping UID and GID to user names and vice versa during the work with dCache.

The meaning of the modifiers follow the PAM specification:


optional The success or failure of this plug-in is only important if it is the only plug-in in the stack associated with this type.

sufficient Success of such a plug-in is enough to satisfy the authentication requirements of the stack of plug-ins (if a prior required plug-in has failed the success of this one is ignored). A failure of this plug-in is not deemed as fatal for the login attempt. If the plug-in succeeds gPlazma2 immediately proceeds with the next plug-in type or returns control to the door if this was the last stack.

required Failure of such a plug-in will ultimately lead to gPlazma2 returning failure but only after the remaining plug-ins for this type have been invoked.

requisite Like required, however, in the case that such a plug-in returns a failure, control is directly returned to the door.


gPlazma2 functionality is configured by combining different types of plug-ins to work together in a way that matches your requirements. For this purpose there are five different types of plug-ins. These types correspond to the keywords auth, map, account, session and identity as described in the previous section. The plug-ins can be configured via properties that may be set in dcache.conf, the layout-file or in gplazma.conf.

auth Plug-ins


The kpwd plug-in authorizes users by username and password, by pairs of DN and FQAN and by Kerberos principals.



Path to dcache.kpwd Default: /etc/dcache/dcache.kpwd


The voms plug-in is an auth plug-in. It can be used to verify X.509 credentials. It takes the certificates and checks their validity by testing them against the trusted CAs. The verified certificates are then stored and passed on to the other plug-ins in the stack.



Path to ca certificates Default: /etc/grid-security/certificates


Path to vomsdir Default: /etc/grid-security/vomsdir

X.509 plug-in

The X.509 is a auth plug-in that extracts X.509 certificate chains from the credentials of a user to be used by other plug-ins.


The jaas uses Java Authentication and Authorization Service and implements username and password based authentication against JAAS configured service. The typical usesage of jaas plugin is authentication with kerberos5. Though it’s possible to use jaas plugin for ldap authentication it’s recommended to use ldap plugin directly.

To configure jaas plugin an extra configuration file defined by dcache.authn.jaas.config property is required. For kerberos5 configuration:

Krb5Gplazma {
   com.sun.security.auth.module.Krb5LoginModule required debug=false useTicketCache=false;

where Krb5Gplazma is the section name to be referenced by gplazma.jaas.name property. For other JAAS -based configurations check desired login module documentation. A single configuration file you may have multiple sections if required.



Path to jass config file Default: /etc/dcache/jgss.conf


jass configuration section name

To complete authentication jaas plugin should be combined with krb5 or mutator mapping plugin.


# krb5 with ldap configuration
auth    optional        jaas gplazma.jaas.name=Krb5Gplazma
map     optional        krb5
map     sufficient      ldap
identity requisite      ldap
session optional        ldap

map Plug-ins


As a map plug-in it maps usernames to UID and GID. And as a session plug-in it adds root and home path information to the session based on the user’s username.



 Path to **dcache.kpwd**
 Default: `/etc/dcache/dcache.kpwd`

The GP2-AUTHZDB takes a username and maps it to UID+GID using the storage-authzdb file.


Path to storage-authzdb Default: /etc/grid-security/storage-authzdb


The authzdb plug-in takes a username and maps it to UID+GID using the storage-authzdb file.



Path to grid-mapfile Default: /etc/grid-security/grid-mapfile


The voms plug-in maps pairs of DN and FQAN to usernames via a vorolemap file.



Path to grid-vorolemap Default: /etc/grid-security/grid-vorolemap


The krb5 plug-in maps a kerberos principal to a username by removing the domain part from the principal.

Example: the Kerberos principal user@KRB-DOMAIN.EXAMPLE.ORG is mapped to the user user.


The nsswitch plug-in uses the system’s nsswitch configuration to provide mapping.

Typically nsswitch plug-in will be combined with vorolemap plug-in, gridmap plug-in or krb5 plug-in:


# Map grid users to local accounts
auth    optional  x509 #1
auth    optional  voms #2
map     requisite vorolemap #3
map     requisite nsswitch #4
session requisite nsswitch #5

In this example following is happening: extract user’s DN (1), extract and verify VOMS attributes (2), map DN+Role to a local account (3), extract uid and gids for a local account (4) and, finally, extract users home directory (5).


The nis uses an existing NIS service to map username+password to a username.



NIS server host Default: nisserv.domain.com


NIS domain Default: domain.com

The result of nis can be used by other plug-ins:


# Map grid or kerberos users to local accounts
auth    optional  x509 #1
auth    optional  voms #2
map     requisite vorolemap #3
map     optional  krb5 #4
map     optional  nis #5
session requisite nis #6

In this example two access methods are considered: grid based and kerberos based. If user comes with grid certificate and VOMS role: extract user’s DN (1), extract and verify VOMS attributes (2), map DN+Role to a local account (3). If user comes with Kerberos ticket: extract local account (4). After this point in both cases we talk to NIS to get uid and gids for a local account (5) and, finally, adding users home directory (6).


The mutator plugin is used to convert principal returned by third-party plugin into a principal, which is understood by gplazma plugins. For example, when the jaas plugin is configured to be used with an ActiveMQ server, then login module specific principal is returned.


# use activemq + mutator + authdb
auth jaas gplazma.jaas.name=ActiveMQ
map optional mutator gplazma.mutator.accept=org.apache.activemq.jaas.UserPrincipal gplazma.mutator.produce=username
map requisite authzdb



The fully qualified java class names of principal that have to the converted.


The gplazma internal principal short-hand name into which provided principal should be converted. The supported short-hand names:

Short name Produced Principal Description
dn GlobusPrincipal To be consumed by Grid specific plugins
kerberos KerberosPrincipal To be consumed bu Kerberos specific plugins
fqan FQANPrincipal To be consumed by Grid-VO specific plugins
name LoginNamePrincipal Login name which requires an aditional mapping to username
username UserNamePrincipalPrincipal which is associated with final login step

account Plug-ins


The argus plug-in bans users by their DN. It talks to your site’s ARGUS system (see https://twiki.cern.ch/twiki/bin/view/EGEE/AuthorizationFramework) to check for banned users.



Path to host certificate Default: /etc/grid-security/hostcert.pem


Path to host key Default: /etc/grid-security/hostkey.pem


Password for host key Default:


Path to CA certificates Default: /etc/grid-security/certificates


URL of PEP service Default: https://localhost:8154/authz


The banfile plug-in bans users by their principal class and the associated name. It is configured via a simple plain text file.


# Ban users by principal
alias dn=org.globus.gsi.gssapi.jaas.GlobusPrincipal
alias kerberos=javax.security.auth.kerberos.KerberosPrincipal
alias fqan=org.dcache.auth.FQANPrincipal
alias name=org.dcache.auth.LoginNamePrincipal

ban name:ernie
ban kerberos:BERT@EXAMPLE.COM
ban com.example.SomePrincipal:Samson

In this example the first line is a comment. Lines 2 to 5 define aliases for principal class names that can then be used in the following banning section. The four aliases defined in this example are actually hard coded into CELL-GPLAZMA, therefore you can use these short names without explicitly defining them in your configuration file. Line 7 to 9 contain ban definitions. Line 9 directly uses the class name of a principal class instead of using an alias.

Please note that the plug-in only supports principals whose assiciated name is a single line of plain text. In programming terms this means the constructor of the principal class has to take exactly one single string parameter.

For the plugin to work, the configuration file has to exist even if it is empty.

After modifying the banfile, you may want to update gplazma.conf to trigger a reload to activate the changes. You can test the result with the explain login command in the gPlazma cell.



Path to configuration file Default: /etc/dcache/ban.conf

To activate the banfile it has to be added to gplazma.conf:


# Map grid or kerberos users to local accounts
auth    optional  x509
auth    optional  voms
map     requisite vorolemap
map     optional  krb5
map     optional  nis
session requisite nis
account requisite banfile

session Plug-ins


The kpwdplug-in adds root and home path information to the session, based on the username.



Path to dcache.kpwd Default: /etc/dcache/dcache.kpwd


The authzdb plug-in adds root and home path information to the session, based and username using the storage-authzdb file.



Path to storage-authzdb Default: /etc/grid-security/storage-authzdb


The nsswitch plug-in adds root and home path information to the session, based on the username using your system’s nsswitch service.

Typically nsswitch plug-in will be combined with vorolemap plug-in, gridmap plug-in or krb5 plug-in:


# Map grid users to local accounts
auth    optional  x509 #1
auth    optional  voms #2
map     requisite vorolemap #3
map     requisite nsswitch #4
session requisite nsswitch #5

In this example following is happening: extract user’s DN (1), extract and verify VOMS attributes (2), map DN+Role to a local account (3), extract uid and gids for a local account (4) and, finally, extract users home directory (5).


The nis plug-in adds root and home path information to the session, based on the username using your site’s NIS service.



`NIS` server host
Default: `nisserv.domain.com`


`NIS` domain
Default: `domain.com`

The result of nis can be used by other plug-ins:


# Map grid or kerberos users to local accounts
auth    optional  x509 #1
auth    optional  voms #2
map     requisite vorolemap #3
map     optional  krb5 #4
map     optional  nis #5
session requisite nis #6

In this example two access methods are considered: grid based and kerberos based. If user comes with grid certificate and VOMS role: extract user’s DN (1), extract and verify VOMS attributes (2), map DN+Role to a local account (3). If user comes with Kerberos ticket: extract local account (4). After this point in both cases we talk to NIS to get uid and gids for a local account (5) and, finally, adding users home directory (6).


The ldap is a map, session and identity plugin. As a map plugin it maps user names to UID and GID. As a session plugin it adds root and home path information to the session. As an identity plugin it supports reverse mapping of UID and GID to user and group names repectively.



`LDAP` server url. Use `ldap://` prefix to connect to plain `LDAP` and `ldaps://` for secured `LDAP`.
Example: `ldaps://example.org:389`


Top level (`base DN`) of the `LDAP` directory tree
Example: `o="Example, Inc.", c=DE`


LDAP subtree containing user information. The path to the user records will be formed using the base DN and the value of this property as a organizational unit (ou) subdirectory.

Default: People

Example: Setting gplazma.ldap.organization=o="Example, Inc.", c=DE and gplazma.ldap.tree.people=People will have the plugin looking in the LDAP directory ou=People, o="Example, Inc.", c=DE for user information.


LDAP subtree containing group information. The path to the group records will be formed using the base DN and the value of this property as a organizational unit (ou) subdirectory.

Default: Groups

Example: Setting gplazma.ldap.organization=o="Example, Inc.", c=DE and gplazma.ldap.tree.groups=Groups will have the plugin looking in the LDAP directory ou=Groups, o="Example, Inc.", c=DE for group information.


LDAP filter expression to find user entries. The filter has to contain the %s exactly once. That occurence will be substituted with the user name before the filter is applied.

Default: (uid=%s)


the user’s home directory. LDAP attribute identifiers surrounded by % will be expanded to their corresponding value. You may also use a literal value or mix literal values and attributes.

Default: %homeDirectory%


the user’s root directory. LDAP attribute identifiers surrounded by % will be expanded to their corresponding value. You may also use a literal value or mix literal values and attributes.

Default: /

As a session plugin the GP2-LDAP assigns two directories to the user’s session: the root directory and the home directory. The root directory is the root of the directory hierarchy visible to the user, while the home directory is the directory the user starts his session in. In default mode, the root directory is set to / and the home directory is set to %homeDirectory%, thus the user starts his session in the home directory, as it is stored on the LDAP server, and is able to go up in the directory hierarchy to /. For a different use-case, for example if dCache is used as a cloud storage, it may be desireable for the users to see only their own storage space. For this use case home-dir can be set to / and root-dir be set to %homeDirectory%. In both path properties any %val% expression will be expanded to the the value of the attribute with the name val as it is stored in the user record on the LDAP server.


Default: false

Allow the ldap plugin to use the user’s (numerical) uid to identify the user if no username is known. If enabled, the plugin uses the uidNumber attribute in LDAP to establish the username for such login attempts.


The omnisession plugin provides an easy and convenient way to provide session information for dCache users. It uses a single configuration file to describe which login attributes (such as home directory, root directory, read-only accounts, etc) are added for dCache users.

It provides a superset of functionality of some other session plugins; specifically, the kpwd and storage-authzdb plugins when used as session plugins: all deployments using a storage-authzdb or kpwd plugin during the session phase may be updated to use the omnisession plugin instead.

The omnisession plugin uses a single configuration file. Without any explicit configuration, this file is located at ${dcache.paths.etc}/omnisession.conf (which expands to /etc/dcache/omnisession.conf by default) but the location may be adjusted by modifying the dcache.paths.etc configuration property or the gplazma.omnisession.file configuration property.

The configuration file may have any number of empty lines. Comments are also supported. Any line that starts with a hash symbol # is treated as a comment and ignored.

All other lines define login attributes that apply to one or more users.

The general format of such lines is


The PREDICATE term describes to which users the attributes apply. These mostly follow a simple TYPE:VALUE format; for example, the predicate username:paul matches all users with a username of paul, similarly, the predicate gid:1000 matches all users with GID of 1000. A complete list of predicate types is given below.

In some cases, a predicate’s value may have spaces. To accomodate such cases, the value may be placed in double-quotes; for example, the predicate dn:"/C=DE/O=GermanGrid/OU=DESY/CN=Alexander Paul Millar" matches all users with that specific distinguished name.

There is a special predicate DEFAULT that matches all users. This may be used to describe attributes that match all users. A file may have at most one DEFAULT line.

The remainder of a non-empty, non-comment line is a white-space separated list of attribute terms. There must be at least one attribute term, with each attribute term describing a login attribute that should be added when the user logs in.

An attribute term generally has the form TYPE:VALUE where TYPE describes what kind of attribute is being defined and VALUE describes the specific value of that type; for example, root:/ indicates that the user’s root directory is / (the root of dCache’s namespace) and home:/Users/paul states that the user’s home directory is /Users/paul. A complete list of attribute types is given below.

Although a line may contain multiple login attributes, there are certain restrictions on those attributes contained on a single line. It is not legal to express the same information more than once; for example, a line with the two terms root:/ root:/data is not valid. This is also not valid even if the values are consistent (e.g., root:/ root:/).

Here is a complete example

username:paul  root:/ home:/Users/paul

In this example, line matches user paul and adds two login attributes: a home directory (with value /Users/paul) and a root directory (with value /).

Login attribute overriding

During the login process, a user is identitied by a set of principals. These principals may match multiple lines in the configuration file. When this happens, login attributes are added in file’s order: a line that matches the user’s principals that appear nearer the top of the file is processed before a matching line that appears further down the file’s contents.

This order matters if the multiple matching lines provide login attributes of the same type; for example, one matching line has a home attribute as does a subsequent matching line.

If this happens then the first attribute (the one nearest the top of the file) is used. Subsequent attributes are ignored for this login attempt.

Here is an example of attribute overriding:

username:paul  home:/Users/paul
group:group-a  root:/ home:/Groups/group-a

In this example, if a user with username paul and who is a member of group group-a logs in, the home directory will be /Users/paul and the root directory will be /. Other members of group-a will have a home directory of /Groups/group-a and a root directory of /.

The DEFAULT is special. It always matches last, irrespective of where it appears in the configuration file. Therefore, if a login attempt matches any lines then those attributes will always take precedence over the DEFAULT set of login attributes.

Although dCache doesn’t care where in the file the DEFAULT predicate is located, but it’s recommended to put it at the end of the file.

The following is another example of attribute overriding, but this time using DEFAULT.

username:paul  home:/Users/paul
group:group-a  home:/Groups/group-a
DEFAULT        root:/ home:/

In this example, the user with username paul has a home directory /Users/paul, members of group-a have a home directory /groups/group-a (except for user paul) and all dCache users have a home directory of / (except for members of group-a and user paul). All users have a root directory of /.

Combining with other session plugins

If the omnisession plugin is combined with other session plugins then omniplugin will refrain from adding attributes that are already defined. Omnisession will add any other (undefined) attributes.

Here’s an example. gPlazma is configured to use both ldap and omnisession as session plugins. When user X logs in the ldap plugin adding a home directory and the omnisession configuration file indicates both a home directory and a root directory for user X. This user will receive the home directory from LDAP and the root directory from omnisession.

The omnisession plugin is successful if it adds at least one login attribute, and fails otherwise. This affects gPlazma configuration (e.g., optional vs sufficient vs requisite). For details, see the section of gPlazma configuration.

Note that users are required to have a home directory attribute and a root directory attribute before their login will be successful.

Handling bad configuration

A line within the configuration file with bad attribute declarations will be marked invalid. The plugin will fail for any user who’s principals match that invalid line’s predicate. The plugin will be successful for users with predicates that only match valid lines and for whom at least one attribute is added.

Here is an example:

username:paul  home:/ home:/Users/paul
DEFAULT        root:/ home:/

The first line is invalid because the home attribute is defined twice. Therefore, the plugin will fail for a login attempt with username paul, but will succeed for other users.

If a line has a badly written predicate then the entire file is considered bad and the plugin will fail for all users.

Here is an example:

user:paul  home:/Users/paul
DEFAULT    root:/ home:/

The predicate user:paul is not valid (it should have be username:paul). Because of this, the plugin will fail for all users.

Predicates catalogue

The omnisession plugin accepts the following predicates.

  • dn The user’s Distinguished Name, which is typically obtained by authenticating via X.509. Example: dn:"/C=DE/O=GermanGrid/OU=DESY/CN=Alexander Paul Millar"
  • email Predicate matches the user’s email address, if known. Example: email:user@example.org matches users with email address user@example.org.
  • gid Predicate matches the user’s gid. There is an optional field that describes whether the match should be limited to users with a matching primary gid, a matching nonprimary gid, or a match gid of either type. Example: gid:1000 matches a user that is a member of the gid 1000 group. gid:1000,primary matches members of the group with gid 1000 if the user has this as their primary gid, gid:1000,nonprimary matches members of the group with gid 1000 if the user has this as their non-primary gid.
  • group Predicate that matches members of the named group. There is an optional field that describes whether the match should be limited to users with a matching primary group, a matching nonprimary group, or a matching group of either use. Example: group:group-a matches a user that is a member of the group-a group. group:group-a,primary matches members of the group-a group if the user has this as their primary group, group:group-a,nonprimary matches members of the group-a group if the user has this as their non-primary gid.
  • fqan Predicate that matches a VOMS FQAN. There is an optional field that describes whether the match should be limited to users with a matching primary FQAN, a matching nonprimary FQAN, or a matching FQAN of either use. Example: fqan:/atlas matches a user that is a member of the /atlas FQAN. fqan:/atlas,primary matches members of the /atlas FQAN if the user has this as their primary FQAN, fqan:/atlas,nonprimary matches members of the /atlas FQAN if the user has this as their non-primary FQAN.
  • kerberos Predicate that matches a Kerberos principal. Example: kerberos:paul@DESY.DE matches users with the Kerberos principal paul@DESY.DE.
  • oidc Predicate that matches an OpenID-Connect sub (“subject”) claim from a specific OP. Example: oidc:83326983-68a3-4f2c-8f0b-385ecd3e97b2@OP matches users identified by the sub claim with the value 83326983-68a3-4f2c-8f0b-385ecd3e97b2 who have authenticated with the OAuth2 Provider configured with the alias OP.
  • oidcgrp Predicate that matches the OpenID-Connect groups claim values. Example: oidcgrp:/main-group matches groups claim that contains a value /main-group.
  • uid Predicate that matches the uid of a user. Example: uid:15691 matches the user with uid 15691.
  • username Predicate that matches the username of a user. Example: username:paul matches the user with username paul.
  • entitlement Predicate that matches an eduPersonEntitlement claim. Example: entitlement:urn:geant:example.org:group:EXAMPLE#example.org matches users that have the eduPersonEntitlement claim urn:geant:helmholtz.de:group:EXAMPLE#login.helmholtz.de
Login attribute catalogue

This section provides a list of all login attributes that the omnisession plugin supports.

The root, home and prefix attributes accept an absolute path as a value. This means those values must start with a /.

  • read-only This attribute limits the user so that the may not modify dCache. Example: read-only.
  • root The user’s root directory. The user will see only a subtree of dCache’s namespace. This works similarly to the chroot command. Example: root:/data/experiment-A that limits the user’s view of the namespace to the /data/expriment-A subtree.
  • home The user’s home directory. In general, this is a directory that is somehow special for the user, although the precise semantics of this attribute is protocol specific. There are network protocols or clients that have no concept of a home directory. Example: home:/Users/paul indicates the user has a home directory of /Users/paul.
  • prefix This attribute limits which part of the namespace a user may access. Unlike the root attribute, the user sees parent directories; however, parent directories appear as if they have a single entry. Example: prefix:/data/experiment-A allows the user access to a specific subtree while preserving paths.
  • max-upload Limit the size of any single uploaded file. The value is a file size that may optionally ISO symbols. Examples: max-upload:5GiB limits uploads to a maximum of five gibibyte (~5.4e9 bytes), max-upload:1TB limits uploads to a maximum of one terabyte (1e12 bytes), max-upload:1048576 limits users to one mibibyte files.

identity Plug-ins


The nsswitsch provides forward and reverse mapping for NFSv4.1 using your system’s nsswitch service.


The nis plug-in forward and reverse mapping for NFSv4.1 using your site’s NIS service.



NIS server host Default: nisserv.domain.com


NIS domain Default: domain.com

Using X509 Certificates

Most plug-ins of gPlazma support X.509 certificates for authentication and authorisation. X.509 certificates are used to identify entities (e.g., persons, hosts) in the Internet. The certificates contain a DN (Distinguished Name) that uniquely describes the entity. To give the certificate credibility it is issued by a CA (Certificate Authority) which checks the identity upon request of the certificate (e.g., by checking the persons id). For the use of X.509 certificates with dCache your users will have to request a certificate from a CA you trust and you need host certificates for every host of your dCache instance.

CA Certificates

To be able to locally verify the validity of the certificates, you need to store the CA certificates on your system. Most operating systems come with a number of commercial CA certificates, but for the Grid you will need the certificates of the Grid CAs. For this, CERN packages a number of CA certificates. These are deployed by most grid sites. By deploying these certificates, you state that you trust the CA’s procedure for the identification of individuals and you agree to act promptly if there are any security issues.

To install the CERN CA certificates follow the following steps:

cd /etc/yum.repos.d/
wget http://grid-deployment.web.cern.ch/grid-deployment/glite/repos/3.2/lcg-CA.repo
yum install lcg-CA

This will create the directory /etc/grid-security/certificates which contains the Grid CA certificates.

Certificates which have been revoked are collected in certificate revocation lists (CRLs). To get the CRLs install the fetch-crl command as described below.

yum install fetch-crl

fetch-crl adds X.509 CRLs to /etc/grid-security/certificates. It is recommended to set up a cron job to periodically update the CRLs.

User Certificate

If you do not have a valid grid user certificate yet, you have to request one from your CA. Follow the instructions from your CA on how to get a certificate. After your request was accepted you will get a URL pointing to your new certificate. Install it into your browser to be able to access grid resources with it. Once you have the certificate in your browser, make a backup and name it userCertificate.p12. Copy the user certificate to the directory ~/.globus/ on your worker node and convert it to usercert.pem and userkey.pem as described below.

openssl pkcs12 -clcerts -nokeys -in <userCertificate>.p12 -out usercert.pem
|Enter Import Password:
|MAC verified OK

During the backup your browser asked you for a password to encrypt the certificate. Enter this password here when asked for a password. This will create your user certificate.

openssl pkcs12 -nocerts -in <userCertificate>.p12 -out userkey.pem
|Enter Import Password:
|MAC verified OK
|Enter PEM pass phrase:

In this step you need to again enter the backup password. When asked for the PEM pass phrase choose a secure password. If you want to use your key without having to type in the pass phrase every time, you can remove it by executing the following command.

openssl rsa -in userkey.pem -out userkey.pem
|Enter pass phrase for userkey.pem:
|writing RSA key

Now change the file permissions to make the key only readable by you and the certificate world readable and only writable by you.

chmod 400 userkey.pem
chmod 644 usercert.pem

Host Certificate

To request a host certificate for your server host, follow again the instructions of your CA.

The conversion to hostcert.pem and hostkey.pem works analogous to the user certificate. For the hostkey you have to remove the pass phrase. How to do this is also explained in the previous section. Finally copy the host*.pem files to /etc/grid-security/ as root and change the file permissions in favour of the user running the grid application.

VOMS Proxy Certificate

For very large groups of people, it is often more convenient to authorise people based on their membership of some group. To identify that they are a member of some group, the certificate owner can create a new short-lived X.509 certificate that includes their membership of various groups. This short-lived certificate is called a proxy-certificate and, if the membership information comes from a VOMS server, it is often referred to as a VOMS-proxy.

cd /etc/yum.repos.d/
wget http://grid-deployment.web.cern.ch/grid-deployment/glite/repos/3.2/glite-UI.repo
yum install glite-security-voms-clients

Creating a VOMS proxy

To create a VOMS proxy for your user certificate you need to execute the voms-proxy-init as a user.


export PATH=/opt/glite/bin/:$PATH
|Enter GRID pass phrase:
|Your identity: /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
|Creating proxy ..................................Done
|Your proxy is valid until Mon Mar  7 22:06:15 2011
Certifying your membership of a VO

You can certify your membership of a VO by using the command voms-proxy-init -voms <yourVO>. This is useful as in dCache authorization can be done by VO (see the section called “Authorizing a VO”). To be able to use the extension -voms <yourVO> you need to be able to access VOMS servers. To this end you need the the VOMS server’s and the CA’s DN. Create a file /etc/grid-security/vomsdir/<VO>/<hostname>.lsc per VOMS server containing on the 1st line the VOMS server’s DN and on the 2nd line, the corresponding CA’s DN. The name of this file should be the fully qualified hostname followed by an .lsc extension and the file must appear in a subdirectory /etc/grid-security/vomsdir/<VO> for each VO that is supported by that VOMS server and by the site.

At http://operations-portal.egi.eu/vo you can search for a VO and find this information.


For example, the file /etc/grid-security/vomsdir/desy/grid-voms.desy.de.lsc contains:


where the first entry is the DN of the DESY VOMS server and the second entry is the DN of the CA which signed the DESY VOMS server’s certificate.

In addition, you need to have a file /opt/glite/etc/vomses containing your VO’s VOMS server.


For DESY the file /opt/glite/etc/vomses should contain the entry

"desy" "grid-voms.desy.de" "15104" "/C=DE/O=GermanGrid/OU=DESY/CN=host/grid-voms.desy.de" "desy" "24"

The first entry “desy” is the real name or a nickname of your VO. “grid-voms.desy.de” is the hostname of the VOMS server. The number “15104” is the port number the server is listening on. The forth entry is the DN of the server’s VOMS certificate. The fifth entry, “desy”, is the VO name and the last entry is the globus version number which is not used anymore and can be omitted.


Use the command voms-proxy-init -voms to create a VOMS proxy with VO “desy”.

voms-proxy-init -voms desy
|Enter GRID pass phrase:
|Your identity: /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
|Creating temporary proxy ....................................................... Done
|Contacting  grid-voms.desy.de:15104 [/C=DE/O=GermanGrid/OU=DESY/CN=host/grid-voms.desy.de] "desy" Done
|Creating proxy .................................... Done
|Your proxy is valid until Mon Mar  7 23:52:13 2011

View the information about your VOMS proxy with voms-proxy-info

|subject   : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe/CN=proxy
|issuer    : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
|identity  : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
|type      : proxy
|strength  : 1024 bits
|path      : /tmp/x509up_u500
|timeleft  : 11:28:02

The last line tells you how much longer your proxy will be valid.

If your proxy is expired you will get

|subject   : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe/CN=proxy
|issuer    : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
|identity  : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
|type      : proxy
|strength  : 1024 bits
|path      : /tmp/x509up_u500
|timeleft  : 0:00:00

The command voms-proxy-info -all gives you information about the proxy and about the VO.

voms-proxy-info -all
subject   : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe/CN=proxy
issuer    : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
identity  : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
type      : proxy
strength  : 1024 bits
path      : /tmp/x509up_u500
timeleft  : 11:24:57
=== VO desy extension information ===
VO        : desy
subject   : /C=DE/O=GermanGrid/OU=DESY/CN=John Doe
issuer    : /C=DE/O=GermanGrid/OU=DESY/CN=host/grid-voms.desy.de
attribute : /desy/Role=NULL/Capability=NULL
attribute : /desy/test/Role=NULL/Capability=NULL
timeleft  : 11:24:57
uri       : grid-voms.desy.de:15104

Use the command voms-proxy-destroy to destroy your VOMS proxy.

|Couldn't find a valid proxy.

Using OpenID Connect

dCache also supports the use of OpenID Connect bearer tokens as a means of authentication.

OpenID Connect is a federated identity system. The dCache users see federated identity as a way to use their existing username & password safely. From a dCache admin’s point-of-view, this involves “outsourcing” responsibility for checking users identities to some external service: you must trust that the service is doing a good job.

OpenID Connect is a simple identity layer on top of the OAuth 2.0 protocol. It enables Clients to verify the identity of the End-User based on the authentication performed by an Authorization Server, as well as to obtain basic profile information about the End-User in an interoperable and REST-like manner.


Common examples of Authorisation servers are Google, Indigo-IAM, Cern-Single-Signon etc.

As of version 2.16, dCache is able to perform authentication based on OpendID Connect credentials on its HTTP end-points. In this document, we outline the configurations necessary to enable this support for OpenID Connect.

OpenID Connect credentials are sent to dCache with Authorisation HTTP Header as follows Authorization: Bearer <yaMMeexxx........>. This bearer token is extracted, validated and verified against a Trusted Authorisation Server (Issue of the bearer token) and is used later to fetch additional user identity information from the corresponding Authorisation Server.

Steps for configuration

In order to configure the OpenID Connect support, we need to

  1. configure the gplazma plugins providing the support for authentication using OpenID credentials and mapping a verified OpenID credential to dCache specific username, uid and gid.
  2. enabling the plugins in gplazma

Gplazma Plugins for OpenId Connect

The support for OpenID Connect in Cache is achieved with the help of two gplazma plugins.

OpenID Authenticate Plugin (oidc)

It takes the extracted OpenID connect credentials (Bearer Token) from the HTTP requests and validates it against a OpenID Provider end-point. The admins need to obtain this information from their trusted OpenID Provider such as Google.

In case of Google, the provider end-point can be obtained from the url of its Discovery Document, e.g. https://accounts.google.com/.well-known/openid-configuration. Hence, the provider end-point in this case would be accounts.google.com.

This end-point has to be appended to the gplazma property gplazma.oidc.hostnames, which should be added to the layouts file. Multiple trusted OpenID providers can be added with space separated list as below.

gplazma.oidc.hostnames = accounts.google.com iam-test.indigo-datacloud.eu

MultiMap plugin (multimap)

dCache requires that authenticated credentials be mapped to posix style username, uid and gid. In case of OpenID credentials, it can be achieved through the new gplazma multimap plugin. This plugin is able to take a verified OpenID credentials in the form of OpenID Subject or the corresponding Email address, and map it to a username, uid, gid etc.

For example,

oidc:9889-1231-2999-12312@GOOGLE username:kermit

email:kermit.the.frog@email.com username:thefrog

In this example, the first line matches users with sub claim 9889-1231-2999-12312 from the OAuth2 Provider GOOGLE and adds the username kermit. The second example matches the email address kermit.the.frog@email.com and adds the username thefrog. In both cases, it is assumed there is an additional mapping from username to uid, gid etc in files like storage-autzdb.

This mapping as shown above can be stored in a gplazma multi-map configuration file. The location of the multimap configuration file can be specified with another gplazma property gplazma.multimap.file. By default it is configured to be located in /etc/dcache/multi-mapfile.

Enable the gplazma plugins

The two plugins above must be enabled in the gplazma.conf.

auth optional oidc

map optional multimap

Restart dCache and check that there are no errors in loading these gplazma plugins.

Third-Party Transfer with OpenID Connect Credentials

Third-party transfer with OpenID Connect Credentials are also possible. dCache performs a token-exchange with the OpenID provider in order and obtain a new delegated bearer token for itself, which it can use (and refresh) to perform Third-party transfer.

In order to perform a token-exchange, it requires the id and secret of a client registered to the OpenID Provider same as that of the bearer token (that was received with the COPY request).

The client-id and client-secret of such a client can be set in the webdav properties as follows,

webdav.oidc.client.ids!provider.hostname : id of a client registered to an OpenId Provider

webdav.oidc.client.secrets!provider.hostname : client-secret corresponding the client-id specified above

Here, provider.hostname must be replaced with a supported OpenID provider like accounts.google.com.

Configuration files

In this section we explain the format of the the storage-authzdb, kpwd and vorolemap files. They are used by the authzdb plug-in, vorolemap plug-in,and kpwd plug-in.


In gPlazma, except for the kpwd plug-in, authorization is a two-step process. First, a username is obtained from a mapping of the user’s DN or his DN and role, then a mapping of username to UID and GID with optional additional session parameters like the root path is performed. For the second mapping usually the file called storage-authzdb is used.

Preparing storage-authzdb

The default location of the storage-authzdb is /etc/grid-security. Before the mapping entries there has to be a line specifying the version of the used file format.


version 2.1

dCache supports versions 2.1 and to some extend 2.2.

Except for empty lines and comments (lines start with #) the configuration lines have the following format:

  authorize <username> (read-only|read-write) <UID> <GID>[,<GID>]* <homedir> <rootdir>

For legacy reasons there may be a third path entry which is ignored by dCache. The username here has to be the name the user has been mapped to in the first step (e.g., by his DN).


authorize john read-write 1001 100 / /data/experiments /

In this example user will be mapped to UID 1001 and GID 100 with read access on the directory /data/experiments. You may choose to set the user’s root directory to /.


 authorize adm read-write 1000 100 / / /

In this case the user will be granted read/write access in any path, given that the file system permissions in CHIMERA also allow the transfer.

The first path is nearly always left as “/”, but it may be used as a home directory in interactive session, as a subdirectory of the root path. Upon login, the second path is used as the user’s root, and a “cd” is performed to the first path. The first path is always defined as being relative to the second path.

Multiple GIDs can be assigned by using comma-separated values for the GID file, as in


authorize john read-write 1001 100,101,200 / / /

The lines of the storage-authzdb file are similar to the “login” lines of the dcache.kpwd file. If you already have a dcache.kwpd file, you can easily create storage-authzdb by taking the lines from your dcache.kpwd file that start with the word login, for example,

login john read-write 1001 100 / /data/experiments /

and replace the word login with authorize. The following line does this for you.

sed "s/^ *login/authorize/" dcache.kpwd|grep "^authorize" > storage-authzdb

The gplazmalite-vorole-mapping plug-in

The second is the storage-authzdb used in other plug-ins. See the above documentation on storage-authdb for how to create the file.

Preparing grid-vorolemap

The file is similar in format to the grid-mapfile, however there is an additional field following the DN (Certificate Subject), containing the FQAN (Fully Qualified Attribute Name).

"/C=DE/O=GermanGrid/OU=DESY/CN=John Doe" "/some-vo" doegroup
"/C=DE/DC=GermanGrid/O=DESY/CN=John Doe" "/some-vo/Role=NULL" doegroup
"/C=DE/DC=GermanGrid/O=DESY/CN=John Doe" "/some-vo/Role=NULL/Capability=NULL" doegroup

Therefore each line has three fields: the user’s DN, the user’s FQAN, and the username that the DN and FQAN combination are to be mapped to.

The FQAN is sometimes semantically referred to as the “role”. The same user can be mapped to different usernames depending on what their FQAN is. The FQAN is determined by how the user creates their proxy, for example, using voms-proxy-init. The FQAN contains the user’s Group, Role (optional), and Capability (optional). The latter two may be set to the string “NULL”, in which case they will be ignored by the plug-in. Therefore the three lines in the example above are equivalent.


If a user is authorized in multiple roles, for example

"/DC=org/DC=doegrids/OU=People/CN=John Doe" "/some-vo/sub-grp" vo_sub_grp_user
"/DC=org/DC=doegrids/OU=People/CN=John Doe" "/some-vo/sub-grp/Role=user" vouser
"/DC=org/DC=doegrids/OU=People/CN=John Doe" "/some-vo/sub-grp/Role=admin" voadmin
"/DC=org/DC=doegrids/OU=People/CN=John Doe" "/some-vo/sub-grp/Role=prod" voprod

he will get the username corresponding to the FQAN found in the proxy that the user creates for use by the client software. If the user actually creates several roles in his proxy, authorization (and subsequent check of path and file system permissions) will be attempted for each role in the order that they are found in the proxy.

In a GRIDFTP URL, the user may also explicitly request a username.


in which case other roles will be disregarded.

Authorizing a VO

Instead of individual DNs, it is allowed to use * or "*" as the first field, such as


"*" "/desy/Role=production/" desyprod

In that case, any DN with the corresponding role will match. It should be noted that a match is first attempted with the explicit DN. Therefore if both DN and "*" matches can be made, the DN match will take precedence. This is true for the revocation matches as well (see below).

Thus a user with subject /C=DE/O=GermanGrid/OU=DESY/CN=John Doe and role /desy/Role=production will be mapped to username desyprod via the above storage-authzdb line with "*" for the DN, except if there is also a line such as

"/C=DE/O=GermanGrid/OU=DESY/CN=John Doe" "/desy/Role=production" desyprod2

in which case the username will be desyprod2.

Revocation Entries

To create a revocation entry, add a line with a dash (-) as the username, such as

"/C=DE/O=GermanGrid/OU=DESY/CN=John Doe" "/desy/production" -

or modify the username of the entry if it already exists. The behaviour is undefined if there are two entries which differ only by username.

Since DN is matched first, if a user would be authorized by his VO membership through a "*" entry, but is matched according to his DN to a revocation entry, authorization would be denied. Likewise if a whole VO were denied in a revocation entry, but some user in that VO could be mapped to a username through his DN, then authorization would be granted.

More Examples

Suppose that there are users in production roles that are expected to write into the storage system data which will be read by other users. In that case, to protect the data the non-production users would be given read-only access. Here in /etc/grid-security/grid-vorolemap the production role maps to username cmsprod, and the role which reads the data maps to cmsuser.

"*" "/cms/uscms/Role=cmsprod" cmsprod "*" "/cms/uscms/Role=cmsuser" cmsuser

The read-write privilege is controlled by the third field in the lines of /etc/grid-security/storage-authzdb

authorize cmsprod  read-write  9811 5063 / /data /
authorize cmsuser  read-only  10001 6800 / /data /


Another use case is when users are to have their own directories within the storage system. This can be arranged within the CELL-GPLAZMA configuration files by mapping each user’s DN to a unique username and then mapping each username to a unique root path. As an example, lines from /etc/grid-security/grid-vorolemap would therefore be written

"/DC=org/DC=doegrids/OU=People/CN=Selby Booth" "/cms" cms821
"/DC=org/DC=doegrids/OU=People/CN=Kenja Kassi" "/cms" cms822
"/DC=org/DC=doegrids/OU=People/CN=Ameil Fauss" "/cms" cms823

and the corresponding lines from /etc/grid-security/storage-authzdb would be

authorize cms821 read-write 10821 7000 / /data/cms821 /
authorize cms822 read-write 10822 7000 / /data/cms822 /
authorize cms823 read-write 10823 7000 / /data/cms823 /

The kpwd plug-in

The section in the gPlazma policy file for the kpwd plug-in specifies the location of the dcache.kpwd file, for example

Example: # dcache.kpwd kpwdPath=“/etc/dcache/dcache.kpwd”

To maintain only one such file, make sure that this is the same location as defined in /usr/share/dcache/defaults/dcache.properties.

Use /usr/share/dcache/examples/gplazma/dcache.kpwd to create this file.

To be able to alter entries in the dcache.kpwd file conveniantly the dcache script offers support for doing this.


dcache kpwd dcuseradd testuser -u 12345 -g 1000 -h / -r / -f / -w read-write -p password

adds this to the kpwd file:

passwd testuser ae39aec3 read-write 12345 1000 / /

There are many more commands for altering the kpwd-file, see the dcache-script help for further commands available.

The gridmap plug-in

Two file locations are defined in the policy file for this plug-in:

# grid-mapfile

Preparing the grid-mapfile

The grid-mapfile is the same as that used in other applications. It can be created in various ways, either by connecting directly to VOMS or GUMS servers, or by hand.

Each line contains two fields: a DN (Certificate Subject) in quotes, and the username it is to be mapped to.


"/C=DE/O=GermanGrid/OU=DESY/CN=John Doe" johndoe

When using the gridmap, the storage-authzdb file must also be configured. See the section called “storage-authzdb” for details.

gPlazma specific dCache configuration

dCache has many parameters that can be used to configure the systems behaviour. You can find all these parameters well documented and together with their default values in the properties files in /usr/share/dcache/defaults/. To use non-default values, you have to set the new values in /etc/dcache/dcache.conf or in the layout file. Do not change the defaults in the properties files! After changing a parameter you have to restart the concerned cells.

Refer to the file gplazma.properties for a full list of properties for gPlazma One commonly used property is gplazma.cell.limits.threads, which is used to set the maximum number of concurrent requests to gPlazma. The default value is 30.

Setting the value for gplazma.cell.limits.threads too high may result in large spikes of CPU activity and the potential to run out of memory. Setting the number too low results in potentially slow login activity.

Enabling Username/Password Access for WEBDAV

This section describes how to activate the Username/Password access for WebDAV. It uses dcache.kwpd file as an example format for storing Username/Password information. First make sure gPlazma2 is enabled in the /etc/dcache/dcache.conf or in the layout file.


Check your WebDAV settings: enable the HTTP access, disallow the anonymous access, disable requesting and requiring the client authentication and activate basic authentication.


Adjust the /etc/dcache/gplazma.conf to use the kpwd plug-in (for more information see also the section called “Plug-ins”.

It will look something like this:

auth optional kpwd
map requisite kpwd
session requisite kpwd

The /etc/dcache/dcache.kpwd file is the place where you can specify the username/password record. It should contain the username and the password hash, as well as UID, GID, access mode and the home, root and fsroot directories:

# set passwd
passwd tanja 6a4cd089 read-write 500 100 / / /

The passwd-record could be automatically generated by the dCache kpwd-utility, for example:

dcache kpwd dcuseradd -u 500 -g 100 -h / -r / -f / -w read-write -p dickerelch tanja

Some file access examples:

curl -u tanja:dickerelch http://webdav-door.example.org:2880/pnfs/

wget --user=tanja --password=dickerelch http://webdav-door.example.org:2880/pnfs/


Roles are a way of describing what capabilities a given user has. They constitute a set of operations defined either explicitly or implicitly which the user who is assigned that role is permitted to exercise.

Roles further allow users to act in more than one capacity without having to change their basic identity. For instance, a “superuser” may wish to act as janedoe for some things, but as an administrator for others, without having to reauthenticate.

While the role framework in dCache is designed to be extensible, there currently exists only one recognized role, that of admin.

To activate the use of the admin role, the following steps are necessary.

1) Define the admin role using the property:


2) Add the admin gid to the set of gids for any user who should have this capability.

3) Add the roles plugin to your gPlazma configuration (usually ‘requisite’ is sufficient):

session requisite roles

Roles are currently used by the dCache Frontend Service to distinguish between regular and admin access. Please refer to that section of this document for further information.