Using the certmap.conf File
Certificate mapping determines how a server scans user entry in the LDAP directory. You can use the certmap.conf to configure how a certificate, designated by name, is mapped to an LDAP entry. You edit this file and add entries to match the structure of your LDAP directory and to list the certificates you want your users to have. Users can be authenticated based on userid, email, or any other value used in the subjectDN. Specifically, the mapping file defines the following information:
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The LDAP tree location the server from where begins its search
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Certificate attributes that the server should use as search criteria when searching for the entry in the LDAP directory
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Whether or not the server goes through an additional verification process
The certificate mapping file is located in the following location:
server_root/userdb/certmap.conf
The file contains one or more named mappings, each applying to a different CA. A mapping has the following syntax:
certmap <name> <issuerDN>
<name>:<property> [<value>]
The first line specifies a name for the entry and the attributes that form the distinguished name found in the CA certificate. You can select any name for the entry. However, the issuerDN must exactly match the issuer DN of the CA that issued the client certificate. For example, the following two issuerDN lines have different space separating the attributes, but the server treats these as two separate entries
certmap sun1 ou=Sun Certificate Authority,o=Sun, c=US
certmap sun2 ou=Sun Certificate Authority, o=Sun, c=US
Note –
If you are using the Sun Java System Directory Server and experiencing problems in matching the issuerDN, check the Directory Server error logs for useful information.
The second and subsequent lines in the named mapping match properties with values. The certmap.conf file has six default properties (you can use the certificate API to customize your own properties):
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The DNComps is a list of comma-separated attributes that determines the location in the LDAP directory the server starts searching for entries that match the user’s information (that is, the owner of the client certificate). The server gathers values for these attributes from the client certificate and uses the values to form an LDAP DN, which then determines where the server starts its search in the LDAP directory. For example, if you set DNComps to use the o and c attributes of the DN, the server starts the search from the o=<org>, c=<country> entry in the LDAP directory, where <org> and <country> are replaced with values from the DN in the certificate.
Note –-
If there isn’t a DNComps entry in the mapping, the server uses either the CmapLdapAttr setting or the entire subject DN in the client certificate (that is, the end-user’s information).
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If the DNComps entry is present but has no value, the server searches the entire LDAP tree for entries matching the filter.
FilterComps is a list of comma-separated attributes that can create a filter by gathering information from the user’s DN in the client certificate. The server uses the values for these attributes to form the search criteria to match entries in the LDAP directory. If the server finds one or more entries in the LDAP directory that match the user’s information gathered from the certificate, the search is successful and the server optionally performs a verification.
For example, if the FilterComps is set to use the email and userid attributes (FilterComps=e,uid), the server searches the directory for an entry with values for email and userid that match the end user’s information collected from the client certificate. Email addresses and userids are good filters because they are usually unique entries in the directory. The filter needs to be specific enough to match unique entry in the LDAP database.
For a list of the x509v3 certificate attributes, see the following table:
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Attribute |
Description |
|---|---|
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Country |
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Organization |
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Common name |
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Location |
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State |
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Organizational unit |
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UNIX/Linux userid |
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Email address |
The attribute names for the filters need to be attribute names from the certificate, not from the LDAP directory. For example, some certificates have an e attribute for the user’s email address; whereas LDAP calls refers to this attribute as mail.
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The verifycert tells the server whether it should compare the client’s certificate with the certificate found in the LDAP directory. It takes two values: on, and off. You should only use this property if your LDAP directory contains certificates. This feature is useful to ensure your end-users have a valid, unrevoked certificate.
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The CmapLdapAttr attribute is a name for the attribute in the LDAP directory that contains subject DNs from all certificates belonging to the user. The default value for this property is certSubjectDN. This attribute is not a standard LDAP attribute. To use this property, you have to extend the LDAP schema. For more information, see Introduction to SSL.
If this property exists in the certmap.conf file, the server searches the entire LDAP directory for an entry whose attribute (named with this property) matches the subject’s full DN (taken from the certificate). If the search does not find any entries, the server retries the search using the DNComps and FilterComps mappings.
This approach to matching a certificate to an LDAP entry is useful when it is difficult to match entries using DNComps and FilterComps.
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The Library property whose value is a pathname to a shared library or DLL. Use this property when you create your own properties using the certificate API. For more information, see the Sun Java System Web Server 6.1 SP9 NSAPI Programmer’s Guide.
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InitFn is a property whose value is the name of an init function from a custom library. Use this property if you create your own properties using the certificate API.
For more information on these properties, refer to the examples described in Sample Mappings.
Creating Custom Properties
You can use the client certificate API to create your own properties. For information on programming and using the client certificate API, see the Sun Java System Web Server 6.1 SP9 NSAPI Programmer’s Guide.
Once you have a custom mapping, you reference the mapping as follows:
<name>:library <path_to_shared_library> <name>:InitFn <name_of_init_function>
For example:
certmap default1 o=Sun Microsystems, c=US default1:library /usr/sun/userdb/plugin.so default1:InitFn plugin_init_fn default1:DNComps ou o c default1:FilterComps l default1:verifycert on
Sample Mappings
The certmap.conf file should have at least one entry. The following examples illustrate the different ways you can use the certmap.conf file.
Example #1
This example represents a certmap.conf file with only one “default” mapping:
certmap default defaultdefault:DNComps ou, o, cdefault:FilterComps e, uiddefault:verifycert on
Using this example, the server starts its search at the LDAP branch point containing the entry ou=<orgunit>, o=<org>, c=<country> where the text within <> is replaced with the values from the subject’s DN in the client certificate.
The server then uses the values for email address and userid from the certificate to search for a match in the LDAP directory. When it finds an entry, the server verifies the certificate by comparing the one the client sent to the one stored in the directory.
Example #2
The following example file has two mappings: one for default and another for the US Postal Service (USPS):
certmap default defaultdefault:DNCompsdefault:FilterComps e, uid
certmap usps ou=United States Postal Service, o=usps, c=USusps:DNComps ou,o,cusps:FilterComps eusps:verifycert on
When the server gets a certificate from someone other than the USPS , it uses the default mapping, which starts at the top of the LDAP tree and searches for an entry matching the client’s userid and email address. If the certificate is from the USPS, the server starts its search at the LDAP branch containing the organizational unit and searches for matching email addresses. Note that if the certificate is from the USPS, the server verifies the certificate; other certificates are not verified.
Caution – The issuer DN (that is, the CA’s information) in the certificate must be identical to the issuer DN listed in the first line of the mapping. In the previous example, a certificate from an issuer DN that is o=United States Postal Service,c=US will not match because there is not a space between the o and the c attributes.
Example #3
The following example uses the CmapLdapAttr property to scan the LDAP database for the certSubjectDN attribute whose value exactly matches the entire subject DN taken from the client certificate.
certmap myco ou=My Company Inc, o=myco, c=USmyco:CmapLdapAttr certSubjectDNmyco:DNComps o, c myco:FilterComps mail, uid myco:verifycert on
If the client certificate subject is:
uid=Walt Whitman, o=LeavesOfGrass Inc, c=US
the server first searches for entries that contain the following information:
certSubjectDN=uid=Walt Whitman, o=LeavesOfGrass Inc, c=US
If one or more matching entries are found, the server proceeds to verify the entries. If no matching entries are found, the server will use DNComps and FilterComps to search for matching entries. In this example, the server would search for uid=Walt Whitman in all entries under o=LeavesOfGrass Inc, c=US.
Note –
This example assumes the LDAP directory contains entries with the certSubjectDN attribute.
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