GUACAMOLE-136: Implement basic support for verifying user identity using Duo.

extensions/guacamole-auth-duo/src/main/resources/styles/duo.css

@@ -0,0 +1,38 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+.duo-signature-response-field iframe {
+    width: 100%;
+    max-width: 620px;
+    height: 330px;
+    border: none;
+}
+
+.duo-signature-response-field iframe {
+    opacity: 1;
+    -webkit-transition: opacity 0.125s;
+    -moz-transition:    opacity 0.125s;
+    -ms-transition:     opacity 0.125s;
+    -o-transition:      opacity 0.125s;
+    transition:         opacity 0.125s;
+}
+
+.duo-signature-response-field.loading iframe {
+    opacity: 0;
+}