feat: apply defaults for customClaims

[xmlking]

Before submitting this PR:

Checklist

• No breaking changes
• Tests pass
• New features have new tests
• Documentation is updated

Breaking changes

Avoid breaking changes and regressions. If you feel it is unavoidable, make it explicit in your PR comment so we can review it and see how to handle it.

Tests

• please make sure your changes pass the current tests (Use the make test or the make watch command).
• if you are introducing a new feature, please write as much tests as possible.

Documentation

Please make sure the documentation is updated accordingly, in particular:

• Workflows. Workflows are Mermaid sequence diagrams
• Schema. The schema in a Mermaid ER diagram
• Environment variables. Please adjust the .env.example file accordingly
• OpenApi specifications. We are using inline JSDoc annotations

[xmlking]

Recreated this original PR
#616

[Copilot]

Pull Request Overview

This PR adds support for default values when extracting custom JWT claims, allowing missing or nil claims to fall back to user-provided defaults.

• Extend the Config and CLI to accept a new CustomClaimsDefaults parameter.
• Update NewCustomClaims and ExtractClaims to store and apply default values.
• Add tests and documentation for the new defaults behavior.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
go/controller/validator_test.go	Initialized CustomClaimsDefaults in the test config
go/controller/custom_claims_test.go	Added test cases covering defaults for custom claims
go/controller/custom_claims.go	Added defaults field and defaultOrNil logic to CustomClaims and ExtractClaims
go/controller/config.go	Exposed CustomClaimsDefaults in the Config struct
go/controller/change_env.go	Unmarshal CustomClaimsDefaults and pass to NewCustomClaims
go/cmd/serve.go	Added --custom-claims-defaults CLI flag
go/cmd/jwt_getter.go	Parsed custom-claims-defaults flag and forwarded defaults
go/cmd/config.go	Loaded CustomClaimsDefaults from CLI context
docs/environment-variables.md	Documented AUTH_JWT_CUSTOM_CLAIMS_DEFAULTS env var

[Copilot]

After writing the error response with c.JSON, the handler should return immediately to prevent further processing.

Suggested change

	c.JSON(http.StatusBadRequest, gin.H{"message": "failed to unmarshal custom claims", "error": err.Error()})
	c.JSON(http.StatusBadRequest, gin.H{"message": "failed to unmarshal custom claims", "error": err.Error()})
	return

[Copilot]

After writing the error response with c.JSON for defaults unmarshal, the handler should return to avoid continuing with an invalid state.

Suggested change

	c.JSON(http.StatusBadRequest, gin.H{"message": "failed to unmarshal custom claims defaults", "error": err.Error()})
	c.JSON(http.StatusBadRequest, gin.H{"message": "failed to unmarshal custom claims defaults", "error": err.Error()})
	return