Group SAML prevents blank NameID on Identity

What

Prevents Identity#extern_uid from being blank for GroupSAML identities.

Why

When SAML for GitLab.com is misconfigured the NameID can be missing and end up as a blank extern_uid. Since we use this to identify which user has signed in this can be problematic, hard for group admins to debug, and hard to for users to fix.

Related

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/10119 Relates to https://gitlab.com/gitlab-org/gitlab-ee/issues/10118

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• EE specific content should be in the top level /ee folder