single sign on - What are the different NameID format used for?

Question

In SAML metadata file there are several NameID format defined, for example:

<NameIDFormat>urn:mace:shibboleth:1.0:nameIdentifier</NameIDFormat>

<NameIDFormat>urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified</NameIDFormat>

<NameIDFormat>urn:oasis:names:tc:SAML:2.0:nameid-format:transient</NameIDFormat>

Can anybody explain what are these used for? What are the differences?

Answer 1

Refer to Section 8.3 of this SAML core pdf of oasis SAML specification.

SP and IdP usually communicate each other about a subject. That subject should be identified through a NAME-IDentifier , which should be in some format so that It is easy for the other party to identify it based on the Format.

All these

1.urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified [default]

2.urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress

3.urn:oasis:names:tc:SAML:2.0:nameid-format:persistent

4.urn:oasis:names:tc:SAML:2.0:nameid-format:transient

are format for the Name Identifiers.

The name format for a transient ID in SAML 1 is urn:mace:shibboleth:1.0:nameIdentifier and in SAML 2 is urn:oasis:names:tc:SAML:2.0:nameid-format:transient

Transient is for [section 8.3.8 of SAML Core]

Indicates that the content of the element is an identifier with transient semantics and SHOULD be treated as an opaque and temporary value by the relying party.

Unspecified can be used and it purely depends on the entities implementation on their own wish.