Authentication: Create endpoint to issue access tokens for Code Suggestions

🧩 Problems to solve

Users of Web IDE need to use their current login session to request access to Code Suggestions feature. We need to create a new GitLab API endpoint to provide this facility.

💡 Solutions

POST /api/v4/code_suggestions/tokens

The access token is:

• A JWT Web Secret (JWS) token
• Valid for 1 hour
• Signed using OIDC private key
• Can be verified using OIDC public key via https://gitlab.com/oauth/discovery/keys

👣 Implementation order

• (This) GitLab API endpoint to issue token - #404427 (closed)
• Model Gateway authentication with JWT token - gitlab-org/modelops/applied-ml/code-suggestions/ai-assist#56 (closed)
• Authenticate Web IDE to Model Gateway - gitlab-web-ide#140 (closed)

📔 References

1. Solution validation issue - gitlab-web-ide#141 (closed)