[feature] Add `created_at` and `error_description` to `/oauth/token` endpoint (#645)

* start fiddling about with oauth server

* start returning more helpful errors from oauth

* test helpful(ish) token errors

* add missing license header

2 files changed, 47 insertions, 3 deletions

diff --git a/internal/oauth/errors.go b/internal/oauth/errors.go
new file mode 100644
index 000000000..25278bdc9
--- /dev/null
+++ b/internal/oauth/errors.go
@@ -0,0 +1,26 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package oauth
+
+import "github.com/superseriousbusiness/oauth2/v4/errors"
+
+// InvalidRequest returns an oauth spec compliant 'invalid_request' error.
+func InvalidRequest() error {
+	return errors.New("invalid_request")
+}
diff --git a/internal/oauth/server.go b/internal/oauth/server.go
index bfe615832..4dcc41ceb 100644
--- a/internal/oauth/server.go
+++ b/internal/oauth/server.go
@@ -25,6 +25,7 @@ import (
 
 	"github.com/sirupsen/logrus"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/oauth2/v4"
 	"github.com/superseriousbusiness/oauth2/v4/errors"
 	"github.com/superseriousbusiness/oauth2/v4/manage"
@@ -52,7 +53,7 @@ const (
 
 // Server wraps some oauth2 server functions in an interface, exposing only what is needed
 type Server interface {
-	HandleTokenRequest(w http.ResponseWriter, r *http.Request) error
+	HandleTokenRequest(r *http.Request) (map[string]interface{}, gtserror.WithCode)
 	HandleAuthorizeRequest(w http.ResponseWriter, r *http.Request) error
 	ValidationBearerToken(r *http.Request) (oauth2.TokenInfo, error)
 	GenerateUserAccessToken(ctx context.Context, ti oauth2.TokenInfo, clientSecret string, userID string) (accessToken oauth2.TokenInfo, err error)
@@ -116,8 +117,25 @@ func New(ctx context.Context, database db.Basic) Server {
 }
 
 // HandleTokenRequest wraps the oauth2 library's HandleTokenRequest function
-func (s *s) HandleTokenRequest(w http.ResponseWriter, r *http.Request) error {
-	return s.server.HandleTokenRequest(w, r)
+func (s *s) HandleTokenRequest(r *http.Request) (map[string]interface{}, gtserror.WithCode) {
+	ctx := r.Context()
+
+	gt, tgr, err := s.server.ValidationTokenRequest(r)
+	if err != nil {
+		help := fmt.Sprintf("could not validate token request: %s", err)
+		return nil, gtserror.NewErrorBadRequest(err, help)
+	}
+
+	ti, err := s.server.GetAccessToken(ctx, gt, tgr)
+	if err != nil {
+		help := fmt.Sprintf("could not get access token: %s", err)
+		return nil, gtserror.NewErrorBadRequest(err, help)
+	}
+
+	data := s.server.GetTokenData(ti)
+	data["created_at"] = ti.GetAccessCreateAt().Unix()
+
+	return data, nil
 }
 
 // HandleAuthorizeRequest wraps the oauth2 library's HandleAuthorizeRequest function