Add a prompt when interacting with an identity server without terms

This adds a prompt whenever we are about to perform some action on a default identity
server (from homeserver .well-known or Riot app config) without terms. This
allows the user to abort or trust the server (storing it in account data).

Fixes https://github.com/vector-im/riot-web/issues/10557

src/utils/IdentityServerUtils.js

@@ -14,6 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { SERVICE_TYPES } from 'matrix-js-sdk';
 import SdkConfig from '../SdkConfig';
 import MatrixClientPeg from '../MatrixClientPeg';
 
@@ -28,3 +29,24 @@ export function useDefaultIdentityServer() {
         base_url: url,
     });
 }
+
+export async function doesIdentityServerHaveTerms(fullUrl) {
+    let terms;
+    try {
+        terms = await MatrixClientPeg.get().getTerms(SERVICE_TYPES.IS, fullUrl);
+    } catch (e) {
+        console.error(e);
+        if (e.cors === "rejected" || e.httpStatus === 404) {
+            terms = null;
+        } else {
+            throw e;
+        }
+    }
+
+    return terms && terms["policies"] && (Object.keys(terms["policies"]).length > 0);
+}
+
+export function doesAccountDataHaveIdentityServer() {
+    const event = MatrixClientPeg.get().getAccountData("m.identity_server");
+    return event && event.getContent() && event.getContent()['base_url'];
+}