Refs #775 -- Pluggable authentication backends (#1447)

* Drag-and-drop: Force csrf_token to be present

* Rough design

* Missing file

* b.visble

* Forms

* Docs

* Tests

* Fix variable

src/pretix/static/pretixcontrol/js/ui/focus.js

@@ -0,0 +1,3 @@
+$(function () {
+	$("input, select, textarea").not(":disabled").focus();
+});

src/pretix/static/pretixcontrol/js/ui/webauthn.js

@@ -163,6 +163,7 @@ const startLogin = async (e) => {
     const transformedAssertionForServer = transformAssertionForServer(assertion);
 
     // post the assertion to the server for verification.
+    $("input, select, textarea").prop("required", false);
     $("#webauthn-response, #id_password").val(JSON.stringify(transformedAssertionForServer));
     $("#webauthn-form").submit();
 };