<--
     * Set ALLOWTOPICCHANGE = VomsGroup
-->

Which binding to use?

Request/Response [< OGSA Authorization Service] < SOAP < {HTTP, HTTPS, HTTP over GSI}

Translating attributes used in VOMS to SAML

Fully Qualified Attribute Name

IetfAttrSyntax ::= SEQUENCE {

Tag List

SAML assertions vs. Attribute Certificate?

References

http://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf

[SAMLBind] Bindings fro the OASIS Security Assertion Markup Language (SAML) V2.0, OASIS Standard, 15 March 2005, available at http://docs.oasis-open.org/security/saml/v2.0/saml-bindings-2.0-os.pdf

[OGSAAuthzService] Welch, Siebenlist, Chadwick, Meder, Pearlman, Use of SAML for OGSA Authorization, September 2003, available at https://forge.gridforum.org/sf/docman/do/downloadDocument/projects.ogsa-authz/docman.root.authz_service/doc9006

a SAML enabled VOMS

Translating attributes used in VOMS to SAML

VOMS releases to users attributes regarding VO membership and role's ownership in form of an Attribute Certificate conforming to RFC3281 (http://www.ietf.org/rfc/rfc3281.txt). Currently it release two kinds of attributes

• Fully Qualified Attribute Name encode the position of the holder inside the vo. A user may be a member of several groups in a vo and may or may not hold a role in the groups he's a member of. This attribute use the following ASN1 syntax

  IetfAttrSyntax ::= SEQUENCE {
  policyAuthorty [0] GeneralNames OPTIONAL,
  values                 SEQUENCE OF CHOICE {
    octets OCTET STRING,
    oid       OBJECT IDENTIFIER,
    string  UTF*String
  }
  }
  

  where policyAuthority contains an encoding of bth the VO which the AC issuer serves and the host which generated the attribute in the form of a URI voname:fqhn:port. This would translate pretty good using SAML 2.0 with

<Attribute xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
           AttributeName="/vo/group/Role=role" AttributeNamespace="vo:host:port">
    </Attribute>

<Attribute xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
           AttributeName="/vo/group/Role=role" AttributeNamespace="vo:host:port">
    </AttributeValue>
</Attribute>

• Generic attributes can be used to specify a attributes that don't map in the group/role paradigm. This attribute use the following ASN1 syntax

TagList ::= SEQUENCE {
policyAuthorty GeneralNames,
tags                    SEQUENCE OF Tag 
}
Tag ::= SEQUENCE {
  name       OCTET STRING
  value       OCTET STRING
  qualifier OCTET STRING
}

<Attribute xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
           AttributeName="attributeName" AttributeNamespace="vo:host:port">
    <AttributeValue>attributeValue</AttributeValue>
</Attribute>

Are SAML assertions as good as Attribute Certificate?

SAML assertions can allocate all the informations contained in Attribute Certificate. Here's a SAML assertion containing an Attribute statement, omitted attribute and signature informations

<Assertion xmlns="urn:oasis:names:tc:SAML:1.0:assertion"
           xmlns:saml="urn:oasis:names:tc:SAML:1.0:assertion"
           xmlns:samlp="urn:oasis:names:tc:SAML:1.0:protocol"
           xmlns:xsd="http://www.w3.org/2001/XMLSchema"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           AssertionID="_f88edc6a61c93bfed776c7290907697e"
           IssueInstant="2006-05-24T16:12:36Z" Issuer="/C=IT/O=INFN/OU=Host/L=CNAF/CN=datatag6.cnaf.infn.it"
           MajorVersion="1" MinorVersion="1">
  <Conditions NotBefore="2006-05-24T16:12:36Z" NotOnOrAfter="2006-05-25T04:12:36Z"/>
  <AttributeStatement>
    <Subject>
      <NameIdentifier Format="urn:oasis:names:tc:SAML:1.1:nameid-format:X509SubjectName">/C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Valerio Venturi/emailAddress=valerio.venturi@cnaf.infn.it</NameIdentifier>
    </Subject>
    <Attribute ...
  </AttributeStatement>
  <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#" ..........
</Assertion>

main concern is with the assertion's subject specification. Attribute Certificate used issuer (certification authority) and serial number of the user's X509 certificate, while saml assertion rely only on the subject of the X509 certificate, unless SubjectConfirmation element is used. Since there are concerns whether dn are good unique identifier, using SubjectConfirmation is suggested.

-- ValerioVenturi - 10 Jul 2006