Adding Content-Type header to the OAuth complete endpoint (#10961)

api4/oauth.go

@@ -538,6 +538,7 @@ func completeOAuth(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	http.Redirect(w, r, redirectUrl, http.StatusTemporaryRedirect)
 }