moved login token signing to LoginToken class

[rbessin]

Pull Request

There are changes (adding res to signatures) from my other ticket which shouldn't be an issue but I couldn't manage to get rid of them since they were in the same file as the changes for this ticket. Hope that isn't an issue. Let me know.

Brief Summary

• Created new loginToken class with static generate method that handles JWT token signing
• Generate returns the signed token and cookie configuration options
• Updated UserController.login() to use LoginToken.generate().

Questions / Considerations for the Future

• Should other cookie options have default values like secure and sameSite? Should they passed in through the cookie options directly?
• Should there be tests for LoginToken.generate()?

Closes #306