GUACAMOLE-1364: Allow both traditional username/password and SSO.

extensions/guacamole-auth-sso/modules/guacamole-auth-sso-base/src/main/resources/html/sso-providers.html

@@ -0,0 +1,7 @@
+<meta name="after" content=".login-ui .login-dialog-middle">
+<div class="sso-providers">
+    <div class="sso-providers-content">
+        {{ 'LOGIN.SECTION_HEADER_SSO_OPTIONS' | translate }}
+        <ul class="sso-provider-list"></ul>
+    </div>
+</div>