Use .well-known to discover a default rendezvous server for use with Sign in with QR

src/components/views/auth/LoginWithQR.tsx

@@ -153,9 +153,11 @@ export default class LoginWithQR extends React.Component<IProps, IState> {
     private generateCode = async (): Promise<void> => {
         let rendezvous: MSC3906Rendezvous;
         try {
+            const fallbackRzServer = this.props.client.getClientWellKnown()?.["io.element.rendezvous"]?.server;
             const transport = new MSC3886SimpleHttpRendezvousTransport<MSC3903ECDHPayload>({
                 onFailure: this.onFailure,
                 client: this.props.client,
+                fallbackRzServer,
             });
 
             const channel = new MSC3903ECDHv2RendezvousChannel<MSC3906RendezvousPayload>(

src/components/views/settings/devices/LoginWithQRSection.tsx

@@ -20,6 +20,7 @@ import {
     IServerVersions,
     UNSTABLE_MSC3882_CAPABILITY,
     Capabilities,
+    IClientWellKnown,
 } from "matrix-js-sdk/src/matrix";
 
 import { _t } from "../../../../languageHandler";
@@ -30,6 +31,7 @@ interface IProps {
     onShowQr: () => void;
     versions?: IServerVersions;
     capabilities?: Capabilities;
+    wellKnown?: IClientWellKnown;
 }
 
 export default class LoginWithQRSection extends React.Component<IProps> {
@@ -43,7 +45,9 @@ export default class LoginWithQRSection extends React.Component<IProps> {
         const capability = UNSTABLE_MSC3882_CAPABILITY.findIn<IMSC3882GetLoginTokenCapability>(this.props.capabilities);
         const msc3882Supported =
             !!this.props.versions?.unstable_features?.["org.matrix.msc3882"] || !!capability?.enabled;
-        const msc3886Supported = !!this.props.versions?.unstable_features?.["org.matrix.msc3886"];
+        const msc3886Supported =
+            !!this.props.versions?.unstable_features?.["org.matrix.msc3886"] ||
+            this.props.wellKnown?.["io.element.rendezvous"]?.server;
         const offerShowQr = msc3882Supported && msc3886Supported;
 
         // don't show anything if no method is available

src/components/views/settings/tabs/user/SessionManagerTab.tsx

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, { useCallback, useContext, useEffect, useRef, useState } from "react";
+import React, { useCallback, useContext, useEffect, useMemo, useRef, useState } from "react";
 import { MatrixClient } from "matrix-js-sdk/src/matrix";
 import { logger } from "matrix-js-sdk/src/logger";
 
@@ -180,6 +180,7 @@ const SessionManagerTab: React.FC = () => {
     const currentUserMember = (userId && matrixClient?.getUser(userId)) || undefined;
     const clientVersions = useAsyncMemo(() => matrixClient.getVersions(), [matrixClient]);
     const capabilities = useAsyncMemo(async () => matrixClient?.getCapabilities(), [matrixClient]);
+    const wellKnown = useMemo(() => matrixClient?.getClientWellKnown(), [matrixClient]);
 
     const onDeviceExpandToggle = (deviceId: ExtendedDevice["device_id"]): void => {
         if (expandedDeviceIds.includes(deviceId)) {
@@ -329,7 +330,12 @@ const SessionManagerTab: React.FC = () => {
                         />
                     </SettingsSubsection>
                 )}
-                <LoginWithQRSection onShowQr={onShowQrClicked} versions={clientVersions} capabilities={capabilities} />
+                <LoginWithQRSection
+                    onShowQr={onShowQrClicked}
+                    versions={clientVersions}
+                    capabilities={capabilities}
+                    wellKnown={wellKnown}
+                />
             </SettingsSection>
         </SettingsTab>
     );

test/components/views/settings/devices/LoginWithQR-test.tsx

@@ -51,6 +51,7 @@ function makeClient() {
         currentState: {
             on: jest.fn(),
         },
+        getClientWellKnown: jest.fn().mockReturnValue({}),
     } as unknown as MatrixClient);
 }
 

test/components/views/settings/devices/LoginWithQRSection-test.tsx

@@ -16,13 +16,13 @@ limitations under the License.
 
 import { render } from "@testing-library/react";
 import { mocked } from "jest-mock";
-import { IServerVersions, MatrixClient, UNSTABLE_MSC3882_CAPABILITY } from "matrix-js-sdk/src/matrix";
+import { IClientWellKnown, IServerVersions, MatrixClient, UNSTABLE_MSC3882_CAPABILITY } from "matrix-js-sdk/src/matrix";
 import React from "react";
 
 import LoginWithQRSection from "../../../../../src/components/views/settings/devices/LoginWithQRSection";
 import { MatrixClientPeg } from "../../../../../src/MatrixClientPeg";
 
-function makeClient() {
+function makeClient(wellKnown: IClientWellKnown) {
     return mocked({
         getUser: jest.fn(),
         isGuest: jest.fn().mockReturnValue(false),
@@ -37,6 +37,7 @@ function makeClient() {
         currentState: {
             on: jest.fn(),
         },
+        getClientWellKnown: jest.fn().mockReturnValue(wellKnown),
     } as unknown as MatrixClient);
 }
 
@@ -49,12 +50,13 @@ function makeVersions(unstableFeatures: Record<string, boolean>): IServerVersion
 
 describe("<LoginWithQRSection />", () => {
     beforeAll(() => {
-        jest.spyOn(MatrixClientPeg, "get").mockReturnValue(makeClient());
+        jest.spyOn(MatrixClientPeg, "get").mockReturnValue(makeClient({}));
     });
 
     const defaultProps = {
         onShowQr: () => {},
         versions: makeVersions({}),
+        wellKnown: {},
     };
 
     const getComponent = (props = {}) => <LoginWithQRSection {...defaultProps} {...props} />;
@@ -114,5 +116,22 @@ describe("<LoginWithQRSection />", () => {
             );
             expect(container).toMatchSnapshot();
         });
+
+        it("MSC3882 r1 + .well-known", async () => {
+            const wellKnown = {
+                "io.element.rendezvous": {
+                    server: "https://rz.local",
+                },
+            };
+            jest.spyOn(MatrixClientPeg, "get").mockReturnValue(makeClient(wellKnown));
+            const { container } = render(
+                getComponent({
+                    versions: makeVersions({}),
+                    capabilities: { [UNSTABLE_MSC3882_CAPABILITY.name]: { enabled: true } },
+                    wellKnown,
+                }),
+            );
+            expect(container).toMatchSnapshot();
+        });
     });
 });

test/components/views/settings/devices/__snapshots__/LoginWithQRSection-test.tsx.snap

@@ -46,6 +46,44 @@ exports[`<LoginWithQRSection /> should render panel MSC3882 + MSC3886 1`] = `
 </div>
 `;
 
+exports[`<LoginWithQRSection /> should render panel MSC3882 r1 + .well-known 1`] = `
+<div>
+  <div
+    class="mx_SettingsSubsection"
+  >
+    <div
+      class="mx_SettingsSubsectionHeading"
+    >
+      <h3
+        class="mx_Heading_h4 mx_SettingsSubsectionHeading_heading"
+      >
+        Sign in with QR code
+      </h3>
+    </div>
+    <div
+      class="mx_SettingsSubsection_content"
+    >
+      <div
+        class="mx_LoginWithQRSection"
+      >
+        <p
+          class="mx_SettingsTab_subsectionText"
+        >
+          You can use this device to sign in a new device with a QR code. You will need to scan the QR code shown on this device with your device that's signed out.
+        </p>
+        <div
+          class="mx_AccessibleButton mx_AccessibleButton_hasKind mx_AccessibleButton_kind_primary"
+          role="button"
+          tabindex="0"
+        >
+          Show QR code
+        </div>
+      </div>
+    </div>
+  </div>
+</div>
+`;
+
 exports[`<LoginWithQRSection /> should render panel MSC3882 r1 + MSC3886 1`] = `
 <div>
   <div