Add Accept header negotiation to relevant API endpoints (#337)

* start centralizing negotiation logic for API

* swagger document nodeinfo endpoint

* go fmt

* document negotiate function

* use content negotiation

* tidy up negotiation logic

* negotiate content throughout client api

* swagger

* remove attachment on Content

* add accept header to test requests

internal/api/client/auth/authorize.go

@@ -21,14 +21,16 @@ package auth
 import (
 	"errors"
 	"fmt"
-	"github.com/sirupsen/logrus"
 	"net/http"
 	"net/url"
 	"strings"
 
+	"github.com/sirupsen/logrus"
+
 	"github.com/gin-contrib/sessions"
 	"github.com/gin-gonic/gin"
 	"github.com/google/uuid"
+	"github.com/superseriousbusiness/gotosocial/internal/api"
 	"github.com/superseriousbusiness/gotosocial/internal/api/model"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
@@ -41,6 +43,11 @@ func (m *Module) AuthorizeGETHandler(c *gin.Context) {
 	l := logrus.WithField("func", "AuthorizeGETHandler")
 	s := sessions.Default(c)
 
+	if _, err := api.NegotiateAccept(c, api.HTMLAcceptHeaders...); err != nil {
+		c.JSON(http.StatusNotAcceptable, gin.H{"error": err.Error()})
+		return
+	}
+
 	// UserID will be set in the session by AuthorizePOSTHandler if the caller has already gone through the authentication flow
 	// If it's not set, then we don't know yet who the user is, so we need to redirect them to the sign in page.
 	userID, ok := s.Get(sessionUserID).(string)