Allow crowd auth to work with Git over HTTPS (like LDAP)

Zendesk: https://gitlab.zendesk.com/agent/tickets/35527

Atlassian Crowd behaves a lot like LDAP and it would be nice if users could authenticate Git over HTTPS using their Crowd credentials. The current implementation allows users to authenticate via the web, but not via Git over HTTPS. The reason we don't do this for other omniauth providers is because many of them are browser-based authentication flows (OAuth, SAML, etc). Since this seems to be a little more like LDAP, we should be able to achieve it.

@patricio You probably know more about how we have LDAP hooked in to provider auth for Git over HTTPS. What do you think?