Add support for role mappings on custom SSO providers.

[Skyler84]

This is done using the role_mappings property.
Roles to be mapped are gotten from the 'warp_groups` oidc claim:

  - name: custom_sso
    label: Custom SSO
    provider:
      type: custom
      client_id: <client_id>
      client_secret: <client_secret>
      issuer_url: <issuer_url>
      scopes: ["email", "profile", "openid", "warp_groups"] #warp_groups is scope name to request for my demo case, which adds a "warpgate_groups" claim to the userinfo
      role_mappings: 
        - ["warpgate:admin", "warpgate:admin"]

This maps the warpgate:admin group from OIDC to the warpgate:admin role.

This video on YouTube demonstrates the functionality

[linhxhust]

I'm looking forward to seeing this PR has been merged.

[Eugeny]

@Skyler84 I have no idea how I've missed this PR, sorry! Refactored the login out into warpgate-core, will test and merge soon

[Skyler84]

thanks! sorry my rust isn't too great yet.