PRIORITY¶

The rules are processed by priority while the number '0' (zero) indicates the highest priority. The higher the number the lower is the priority. A missing value indicates the lowest priority. The rules processing is stopped when a matched rule is found and no further rules are checked.

Internally the priority is treated as unsigned 32bit integer, using a priority value larger than 4294967295 will cause an error.

If multiple rules have the same priority and only one of the related matching rules applies, this rule will be chosen. If there are multiple rules with the same priority which matches, one is chosen but which one is undefined. To avoid this undefined behavior either use different priorities or make the matching rules more specific e.g. by using distinct <ISSUER> patterns.

MATCHING RULE¶

The matching rule is used to select a certificate to which the mapping rule should be applied. It uses a system similar to the one used by “pkinit_cert_match” option of MIT Kerberos. It consists of a keyword enclosed by '<' and '>' which identified a certain part of the certificate and a pattern which should be found for the rule to match. Multiple keyword pattern pairs can be either joined with '&&' (and) or '||' (or).

Given the similarity to MIT Kerberos the type prefix for this rule is 'KRB5'. But 'KRB5' will also be the default for “matching rules” so that "<SUBJECT>.*,DC=MY,DC=DOMAIN" and "KRB5:<SUBJECT>.*,DC=MY,DC=DOMAIN" are equivalent.

The available options are:

<SUBJECT>regular-expression

<ISSUER>regular-expression

<KU>key-usage

<EKU>extended-key-usage

<SAN>regular-expression

<SAN:Principal>regular-expression

<SAN:ntPrincipalName>regular-expression

<SAN:pkinit>regular-expression

<SAN:dotted-decimal-oid>regular-expression

<SAN:otherName>base64-string

<SAN:rfc822Name>regular-expression

<SAN:dNSName>regular-expression

<SAN:x400Address>base64-string

<SAN:directoryName>regular-expression

<SAN:ediPartyName>base64-string

<SAN:uniformResourceIdentifier>regular-expression

<SAN:iPAddress>regular-expression

<SAN:registeredID>regular-expression

MAPPING RULE¶

The mapping rule is used to associate a certificate with one or more accounts. A Smartcard with the certificate and the matching private key can then be used to authenticate as one of those accounts.

Currently SSSD basically only supports LDAP to lookup user information (the exception is the proxy provider which is not of relevance here). Because of this the mapping rule is based on LDAP search filter syntax with templates to add certificate content to the filter. It is expected that the filter will only contain the specific data needed for the mapping and that the caller will embed it in another filter to do the actual search. Because of this the filter string should start and stop with '(' and ')' respectively.

In general it is recommended to use attributes from the certificate and add them to special attributes to the LDAP user object. E.g. the 'altSecurityIdentities' attribute in AD or the 'ipaCertMapData' attribute for IPA can be used.

This should be preferred to read user specific data from the certificate like e.g. an email address and search for it in the LDAP server. The reason is that the user specific data in LDAP might change for various reasons would break the mapping. On the other hand it would be hard to break the mapping on purpose for a specific user.

The default “mapping rule” type is 'LDAP' which can be added as a prefix to a rule like e.g. 'LDAP:(userCertificate;binary={cert!bin})'. There is an extension called 'LDAPU1' which offer more templates for more flexibility. To allow older versions of this library to ignore the extension the prefix 'LDAPU1' must be used when using the new templates in a “mapping rule” otherwise the old version of this library will fail with a parsing error. The new templates are described in section the section called “LDAPU1 extension”.

The templates to add certificate data to the search filter are based on Python-style formatting strings. They consist of a keyword in curly braces with an optional sub-component specifier separated by a '.' or an optional conversion/formatting option separated by a '!'. Allowed values are:

{issuer_dn[!((ad|ad_x500)|ad_ldap|nss_x500|(nss|nss_ldap))]}

{subject_dn[!((ad|ad_x500)|ad_ldap|nss_x500|(nss|nss_ldap))]}

{cert[!(bin|base64)]}

{subject_principal[.short_name]}

{subject_pkinit_principal[.short_name]}

{subject_nt_principal[.short_name]}

{subject_rfc822_name[.short_name]}

{subject_dns_name[.short_name]}

{subject_uri}

{subject_ip_address}

{subject_x400_address}

{subject_directory_name[!((ad|ad_x500)|ad_ldap|nss_x500|(nss|nss_ldap))]}

{subject_ediparty_name}

{subject_registered_id}

LDAPU1 extension

DOMAIN LIST¶

If the domain list is not empty users mapped to a given certificate are not only searched in the local domain but in the listed domains as well as long as they are know by SSSD. Domains not know to SSSD will be ignored.