[feature] oob oauth token support (#889)

* move helpful advice into oauth server

* rewrite HandleAuthorizeRequest to allow oob

internal/api/client/auth/oob.go

@@ -0,0 +1,111 @@
+/*
+   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 auth
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+
+	"github.com/gin-contrib/sessions"
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/api"
+	"github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+)
+
+func (m *Module) OobHandler(c *gin.Context) {
+	host := config.GetHost()
+	instance, errWithCode := m.processor.InstanceGet(c.Request.Context(), host)
+	if errWithCode != nil {
+		api.ErrorHandler(c, errWithCode, m.processor.InstanceGet)
+		return
+	}
+
+	instanceGet := func(ctx context.Context, domain string) (*model.Instance, gtserror.WithCode) { return instance, nil }
+
+	oobToken := c.Query("code")
+	if oobToken == "" {
+		err := errors.New("no 'code' query value provided in callback redirect")
+		api.ErrorHandler(c, gtserror.NewErrorBadRequest(err, err.Error(), oauth.HelpfulAdvice), instanceGet)
+		return
+	}
+
+	s := sessions.Default(c)
+
+	errs := []string{}
+
+	scope, ok := s.Get(sessionScope).(string)
+	if !ok {
+		errs = append(errs, fmt.Sprintf("key %s was not found in session", sessionScope))
+	}
+
+	userID, ok := s.Get(sessionUserID).(string)
+	if !ok {
+		errs = append(errs, fmt.Sprintf("key %s was not found in session", sessionUserID))
+	}
+
+	if len(errs) != 0 {
+		errs = append(errs, oauth.HelpfulAdvice)
+		api.ErrorHandler(c, gtserror.NewErrorBadRequest(errors.New("one or more missing keys on session during OobHandler"), errs...), m.processor.InstanceGet)
+		return
+	}
+
+	user, err := m.db.GetUserByID(c.Request.Context(), userID)
+	if err != nil {
+		m.clearSession(s)
+		safe := fmt.Sprintf("user with id %s could not be retrieved", userID)
+		var errWithCode gtserror.WithCode
+		if err == db.ErrNoEntries {
+			errWithCode = gtserror.NewErrorBadRequest(err, safe, oauth.HelpfulAdvice)
+		} else {
+			errWithCode = gtserror.NewErrorInternalError(err, safe, oauth.HelpfulAdvice)
+		}
+		api.ErrorHandler(c, errWithCode, instanceGet)
+		return
+	}
+
+	acct, err := m.db.GetAccountByID(c.Request.Context(), user.AccountID)
+	if err != nil {
+		m.clearSession(s)
+		safe := fmt.Sprintf("account with id %s could not be retrieved", user.AccountID)
+		var errWithCode gtserror.WithCode
+		if err == db.ErrNoEntries {
+			errWithCode = gtserror.NewErrorBadRequest(err, safe, oauth.HelpfulAdvice)
+		} else {
+			errWithCode = gtserror.NewErrorInternalError(err, safe, oauth.HelpfulAdvice)
+		}
+		api.ErrorHandler(c, errWithCode, instanceGet)
+		return
+	}
+
+	// we're done with the session now, so just clear it out
+	m.clearSession(s)
+
+	c.HTML(http.StatusOK, "oob.tmpl", gin.H{
+		"instance": instance,
+		"user":     acct.Username,
+		"oobToken": oobToken,
+		"scope":    scope,
+	})
+}