refactor: use struct types for claim related types (#283)

* oidc: add regression tests for token claim json

this helps to verify that the same JSON is produced,
after these types are refactored.

* refactor: use struct types for claim related types

BREAKING CHANGE:
The following types are changed from interface to struct type:

- AccessTokenClaims
- IDTokenClaims
- IntrospectionResponse
- UserInfo and related types.

The following methods of OPStorage now take a pointer to a struct type,
instead of an interface:

- SetUserinfoFromScopes
- SetUserinfoFromToken
- SetIntrospectionFromToken

The following functions are now generic, so that type-safe extension
of Claims is now possible:

- op.VerifyIDTokenHint
- op.VerifyAccessToken
- rp.VerifyTokens
- rp.VerifyIDToken

- Changed UserInfoAddress to pointer in UserInfo and
IntrospectionResponse.
This was needed to make omitempty work correctly.
- Copy or merge maps in IntrospectionResponse and SetUserInfo

* op: add example for VerifyAccessToken

* fix: rp: wrong assignment in WithIssuedAtMaxAge

WithIssuedAtMaxAge assigned its value to v.maxAge, which was wrong.
This change fixes that by assiging the duration to v.maxAgeIAT.

* rp: add VerifyTokens example

* oidc: add standard references to:

- IDTokenClaims
- IntrospectionResponse
- UserInfo

* only count coverage for `./pkg/...`

pkg/op/userinfo.go

@@ -34,7 +34,7 @@ func Userinfo(w http.ResponseWriter, r *http.Request, userinfoProvider UserinfoP
 		http.Error(w, "access token invalid", http.StatusUnauthorized)
 		return
 	}
-	info := oidc.NewUserInfo()
+	info := new(oidc.UserInfo)
 	err = userinfoProvider.Storage().SetUserinfoFromToken(r.Context(), info, tokenID, subject, r.Header.Get("origin"))
 	if err != nil {
 		httphelper.MarshalJSONWithStatus(w, err, http.StatusForbidden)
@@ -81,9 +81,9 @@ func getTokenIDAndSubject(ctx context.Context, userinfoProvider UserinfoProvider
 		}
 		return splitToken[0], splitToken[1], true
 	}
-	accessTokenClaims, err := VerifyAccessToken(ctx, accessToken, userinfoProvider.AccessTokenVerifier(ctx))
+	accessTokenClaims, err := VerifyAccessToken[*oidc.AccessTokenClaims](ctx, accessToken, userinfoProvider.AccessTokenVerifier(ctx))
 	if err != nil {
 		return "", "", false
 	}
-	return accessTokenClaims.GetTokenID(), accessTokenClaims.GetSubject(), true
+	return accessTokenClaims.JWTID, accessTokenClaims.Subject, true
 }