Draft: (WIP) Add IAM Service OAuth feature flag for JWT authentication

Daniele Braccianirequested to merge
db/580758/new-auth-iam-accept-external-oauth-token into master

What does this MR do and why?

Add IAM Service OAuth feature flag for JWT authentication

Introduces iam_svc_oauth feature flag to enable JWT authentication from external IAM service as an alternative to Doorkeeper OAuth.

Changes:

  • Add feature flag iam_svc_oauth (disabled by default)
  • Add Gitlab::Auth::IamJwt module with error hierarchy
  • Add Gitlab::Auth::IamJwt::Token class for validated JWTs
  • Add Gitlab::Auth::IamJwt::JwksClient for RS256 key fetching/caching
  • Add Auth::IamJwtValidationService for JWT signature verification
  • Integrate IAM JWT check into AuthFinders before OAuth
  • Add IAM JWT attributes to Current class
  • Add ApplicationSetting fields for IAM service configuration

Related to: #580758

WIP

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Before After

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