Add email claim to ID token

[Copilot]

Summary

Fixes the issue where the mock OAuth2 server was not returning an email claim in the ID token. The ID token now includes the email claim along with the standard OpenID Connect claims.

Changes

The GenerateIDToken function has been updated to accept an email parameter and include it in the token claims. The email is automatically generated based on the client ID using the format {clientID}@example.com.

Before

ID tokens contained only these claims:

• aud, exp, iat, iss, nonce, sub

After

ID tokens now include:

• aud, exp, iat, iss, nonce, sub, email

Example

When a client exchanges an authorization code for tokens with client ID test-client, the decoded ID token payload now looks like:

{
  "iss": "http://localhost:8080",
  "sub": "user-test-client",
  "aud": "test-client",
  "exp": 1760286080,
  "iat": 1760282480,
  "nonce": "randomNonce123",
  "email": "[email protected]"
}

Testing

• Updated all existing tests to pass the email parameter
• Added verification that the email claim is present in generated ID tokens
• All tests pass successfully with no regressions

Files Modified

• internal/jwt/jwt.go - Added email parameter to GenerateIDToken and included email in claims
• internal/jwt/jwt_test.go - Updated tests to verify email claim
• internal/handlers/token.go - Updated to generate and pass email based on client ID
• pkg/oauth/google.go - Updated OAuth provider to include email in ID tokens

Original prompt

---

This section details on the original issue you should resolve

<issue_title>shoud return email in claims</issue_title>
<issue_description>The mock server should return email in the id token claims - it is currently only returning

aud, exp, iat, iss, nonce, sub
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

Fixes #6

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