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When integrating OIDC (OpenID Connect) with gateway solutions, there are some critical considerations to keep in mind.

Important Notes

Issue 1: OIDC Parameter Transmission Mode

Issue: By default, OIDC authentication returns parameters using URL fragments (#). However, fragment values remain in the browser and are not sent to the server. This causes authentication errors when a gateway solution is added in between.
Solution: You need to set the response_mode parameter to “query” in your OIDC configuration. This way, parameters are transmitted as query parameters (?) instead of fragments and are successfully transmitted to the server.
Configuration:
  • For Keycloak: In client settings, under “Advanced Settings”, set “Response Mode” value to “query”.
  • For other OIDC providers: Add “response_mode=query” parameter in the relevant client configuration.

Issue 2: Header Size Limitations with Nginx Ingress Controller

Issue: When using OIDC with Nginx Ingress Controller, authentication cookies and headers may exceed default buffer size limits. This causes 400 Bad Request errors or truncated headers during authentication. Solution: Increase buffer size settings in your Nginx Ingress Controller configuration:
These settings ensure that Nginx Ingress Controller properly handles the larger headers commonly encountered with OIDC authentication tokens and cookies.