RedirectTo in AuthorizeRequest and Code JSON field tag corrrected in TokenRequest

[daic0r]

What kind of change does this PR introduce?

This PR

• adds a RedirectTo field to types.AuthorizeRequest. This will be passed along in a request to the /auth/v1/authorize endpoint.
• corrects the name of the JSON field tag of Code in types.TokenRequest

What is the current behavior?

Currently, there is no RedirectTo field in types.AuthorizeRequest: #4
The field Code in types.TokenRequest has a wrong JSON name in the struct field tag: #5

What is the new behavior?

• Callback route can be passed to the /auth/v1/authorize endpoint
• Code exchange for PKCE will now work because the Code field's JSON name will be correct when /auth/v1/token is called.

[kwoodhouse93]

Thanks for your contribution!

The change looks good, only one comment - can we rebase and scope it to only adding the redirect URL here, please? Another PR has addressed the auth_code fix 🙂