Error After Upgrade: SAML Missing the NameID Element

Problem

You've upgraded Mattermost, and now you're getting an error within Mattermost related to SAML that looks like this:

{"path": "/login/sso/saml", "request_id": "enjsecm5xjrhfdnone3m6y84dc", "ip_addr": "1.1.1.1", "user_id": "", "method": "POST", "err_where": "SamlInterfaceLibImpl.DoLogin", "http_code": 302, "err_details": "err=missing NameID element"}

Or when attempting to log in you're presented with the below error:

  An error occurred while parsing the response from the Identity Provider. Please
  contact your System Administrator.

This error exists because your SAML provider is most likely not returning the NameID attribute which is required with the new SAML library in Mattermost Server v5.29.2 and above.

Solution

Follow the steps here and make sure the claim ID rules contain a Name ID as outlined in step 3 of the documentation. It will end up looking like the screenshot below: