Start supporting OAuth 2.0 authentication API

locales/en/app.json

@@ -90,6 +90,7 @@
     "e2ee_unsupported_description": "Your web browser does not support encrypted calls. Supported browsers include Chrome, Safari, and Firefox 117+.",
     "generic": "Something went wrong",
     "generic_description": "Submitting debug logs will help us track down the problem.",
+    "homeserver_misconfig": "Misconfigured homeserver",
     "insufficient_capacity": "Insufficient capacity",
     "insufficient_capacity_description": "The server has reached its maximum capacity and you cannot join the call at this time. Try again later, or contact your server admin if the problem persists.",
     "matrix_rtc_focus_missing": "The server is not configured to work with {{brand}}. Please contact your server admin (Domain: {{domain}}, Error Code: {{ errorCode }}).",

src/App.tsx

@@ -20,6 +20,7 @@ import { logger } from "matrix-js-sdk/lib/logger";
 
 import { HomePage } from "./home/HomePage";
 import { LoginPage } from "./auth/LoginPage";
+import { OidcRedirectPage } from "./auth/OidcRedirectPage";
 import { RegisterPage } from "./auth/RegisterPage";
 import { RoomPage } from "./room/RoomPage";
 import { ClientProvider } from "./ClientContext";
@@ -88,6 +89,7 @@ export const App: FC<Props> = ({ vm }) => {
             <Routes>
               <SentryRoute path="/" element={<HomePage />} />
               <SentryRoute path="/login" element={<LoginPage />} />
+              <SentryRoute path="/after_login" element={<OidcRedirectPage />} />
               <SentryRoute path="/register" element={<RegisterPage />} />
               <SentryRoute path="*" element={<RoomPage />} />
             </Routes>

src/Avatar.test.tsx

@@ -21,6 +21,7 @@ const TestComponent: FC<
     <ClientContextProvider
       value={{
         state: "valid",
+        oidcClientConfig: null,
         disconnected: false,
         supportedFeatures: {
           reactions: true,

src/ClientContext.tsx

@@ -1,5 +1,5 @@
 /*
-Copyright 2021-2024 New Vector Ltd.
+Copyright 2021-2025 New Vector Ltd.
 
 SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
@@ -19,7 +19,7 @@ import {
 import { useNavigate } from "react-router-dom";
 import { logger } from "matrix-js-sdk/lib/logger";
 import { type ISyncStateData, type SyncState } from "matrix-js-sdk/lib/sync";
-import { ClientEvent, type MatrixClient } from "matrix-js-sdk";
+import { ClientEvent, type OidcClientConfig, type MatrixClient } from "matrix-js-sdk";
 
 import type { WidgetApi } from "matrix-widget-api";
 import { ErrorPage } from "./FullScreenView";
@@ -29,6 +29,7 @@ import {
   RegistrationType,
 } from "./analytics/PosthogAnalytics";
 import { useEventTarget } from "./useEvents";
+import { getAuthMetadata } from "./utils/oidc/discovery";
 import { OpenElsewhereError } from "./RichError";
 
 declare global {
@@ -42,6 +43,7 @@ export type ClientState = ValidClientState | ErrorState;
 
 export type ValidClientState = {
   state: "valid";
+  oidcClientConfig: OidcClientConfig | null,
   authenticated?: AuthenticatedClient;
   // 'Disconnected' rather than 'connected' because it tracks specifically
   // whether the client is supposed to be connected but is not
@@ -74,17 +76,20 @@ export const useClientState = (): ClientState | undefined => use(ClientContext);
 export function useClient(): {
   client?: MatrixClient;
   setClient?: (client: MatrixClient, session: Session) => void;
+  oidcClientConfig: OidcClientConfig | null | undefined;
 } {
   let client;
   let setClient;
+  let oidcClientConfig;
 
   const clientState = useClientState();
   if (clientState?.state === "valid") {
     client = clientState.authenticated?.client;
     setClient = clientState.setClient;
+    oidcClientConfig = clientState.oidcClientConfig;
   }
 
-  return { client, setClient };
+  return { client, setClient, oidcClientConfig };
 }
 
 // Plain representation of the `ClientContext` as a helper for old components that expected an object with multiple fields.
@@ -140,6 +145,12 @@ interface Props {
 export const ClientProvider: FC<Props> = ({ children }) => {
   const navigate = useNavigate();
 
+  // null = no OIDC config, undefined = loading
+  const [oidcClientConfig, setOidcClientConfig] = useState<
+    OidcClientConfig | null | undefined
+  >(undefined);
+  const [oidcErr, setOidcErr] = useState<Error | undefined>(undefined);
+
   // null = signed out, undefined = loading
   const [initClientState, setInitClientState] = useState<
     InitResult | null | undefined
@@ -153,6 +164,11 @@ export const ClientProvider: FC<Props> = ({ children }) => {
     if (initializing.current) return;
     initializing.current = true;
 
+    if (!widget) {
+      // TODO: spec says this may change over time & should be refreshed upon cache expiry
+      getAuthMetadata().then(setOidcClientConfig, setOidcErr);
+    }
+
     loadClient()
       .then((initResult) => {
         setInitClientState(initResult);
@@ -251,12 +267,18 @@ export const ClientProvider: FC<Props> = ({ children }) => {
   const [supportsReactions, setSupportsReactions] = useState(false);
   const [supportsThumbnails, setSupportsThumbnails] = useState(false);
 
-  const state: ClientState | undefined = useMemo(() => {
+  const state = useMemo((): ClientState | undefined => {
-    if (alreadyOpenedErr) {
+    const error = alreadyOpenedErr || oidcErr;
-      return { state: "error", error: alreadyOpenedErr };
+    if (error) {
+      return { state: "error", error };
     }
 
-    if (initClientState === undefined) return undefined;
+    if (
+      initClientState === undefined ||
+      oidcClientConfig === undefined
+    ) {
+      return undefined;
+    }
 
     const authenticated =
       initClientState === null
@@ -270,6 +292,7 @@ export const ClientProvider: FC<Props> = ({ children }) => {
 
     return {
       state: "valid",
+      oidcClientConfig,
       authenticated,
       setClient,
       disconnected: isDisconnected,
@@ -280,6 +303,8 @@ export const ClientProvider: FC<Props> = ({ children }) => {
     };
   }, [
     alreadyOpenedErr,
+    oidcErr,
+    oidcClientConfig,
     changePassword,
     initClientState,
     logout,
@@ -345,8 +370,9 @@ export const ClientProvider: FC<Props> = ({ children }) => {
     };
   }, [initClientState, onSync]);
 
-  if (alreadyOpenedErr) {
+  const error = alreadyOpenedErr || oidcErr;
-    return <ErrorPage widget={widget} error={alreadyOpenedErr} />;
+  if (error) {
+    return <ErrorPage widget={widget} error={error} />;
   }
 
   return <ClientContext value={state}>{children}</ClientContext>;

src/RichError.tsx

@@ -6,7 +6,7 @@ Please see LICENSE in the repository root for full details.
 */
 
 import { useTranslation } from "react-i18next";
-import { PopOutIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
+import { ErrorIcon, PopOutIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
 
 import type { FC, ReactNode } from "react";
 import { ErrorView } from "./ErrorView";
@@ -51,3 +51,29 @@ export class OpenElsewhereError extends RichError {
     super("App opened in another tab", <OpenElsewhere />);
   }
 }
+
+const HomeserverMisconfig: FC<{message?: string}> = (props) => {
+  const { t } = useTranslation();
+
+  // TODO: don't want to show "Return to home screen" button for an error as fatal as this
+  return (
+    <ErrorView
+      widget={widget}
+      Icon={ErrorIcon}
+      title={t("error.homeserver_misconfig")}
+      fatal={true}
+    >
+      {props.message && (
+        <p>
+          {props.message}
+        </p>
+      )}
+    </ErrorView>
+  );
+};
+
+export class HomeserverMisconfigError extends RichError {
+  public constructor(message?: string) {
+    super(message || "Unknown error", <HomeserverMisconfig message={message} />);
+  }
+}

src/auth/LoginPage.tsx

@@ -1,11 +1,11 @@
 /*
-Copyright 2021-2024 New Vector Ltd.
+Copyright 2021-2025 New Vector Ltd.
 
 SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type FC, type FormEvent, useCallback, useRef, useState } from "react";
+import { type FC, type FormEvent, type ReactElement, useCallback, useRef, useState } from "react";
 import { useNavigate, useLocation } from "react-router-dom";
 import { Trans, useTranslation } from "react-i18next";
 import { Button } from "@vector-im/compound-web";
@@ -19,13 +19,14 @@ import { usePageTitle } from "../usePageTitle";
 import { PosthogAnalytics } from "../analytics/PosthogAnalytics";
 import { Config } from "../config/Config";
 import { Link } from "../button/Link";
+import { LoadingPage } from "../FullScreenView";
+import { getOidcClientId } from "../utils/oidc/registerClient";
+import { startOidcLogin } from "../utils/oidc/authorize";
 
 export const LoginPage: FC = () => {
   const { t } = useTranslation();
   usePageTitle(t("login_title"));
 
-  const { client, setClient } = useClient();
-  const login = useInteractiveLogin(client);
   const homeserver = Config.defaultHomeserverUrl(); // TODO: Make this configurable
   const usernameRef = useRef<HTMLInputElement>(null);
   const passwordRef = useRef<HTMLInputElement>(null);
@@ -36,19 +37,23 @@ export const LoginPage: FC = () => {
 
   // TODO: Handle hitting login page with authenticated client
 
-  const onSubmitLoginForm = useCallback(
+  let node: ReactElement;
-    (e: FormEvent<HTMLFormElement>) => {
+  const { client, setClient, oidcClientConfig } = useClient();
-      e.preventDefault();
+  if (oidcClientConfig === null) {
-      setLoading(true);
+    const login = useInteractiveLogin(client);
+    const onSubmitLoginForm = useCallback(
+      async (e: FormEvent<HTMLFormElement>): Promise<void> => {
+        e.preventDefault();
+        setLoading(true);
 
-      if (!homeserver || !usernameRef.current || !passwordRef.current) {
+        if (!homeserver) {
-        setError(Error("Login parameters are undefined"));
+          setError(Error("Login parameters are undefined"));
-        setLoading(false);
+          setLoading(false);
-        return;
+          return;
-      }
+        }
 
-      login(homeserver, usernameRef.current.value, passwordRef.current.value)
+        try {
-        .then(async ([client, session]) => {
+          const [client, session] = await login(homeserver, usernameRef.current?.value ?? "", passwordRef.current?.value ?? "");
           if (!setClient) {
             return;
           }
@@ -66,20 +71,84 @@ export const LoginPage: FC = () => {
             await navigate("/");
           }
           PosthogAnalytics.instance.eventLogin.track();
-        })
+        } catch (error: any) {
-        .catch((error) => {
           setError(error);
           setLoading(false);
-        });
+        }
-    },
+      },
-    [login, location, navigate, homeserver, setClient],
+      [login, location, navigate, homeserver, setClient],
-  );
+    );
-  // we need to limit the length of the homserver name to not cover the whole loginview input with the string.
+    // we need to limit the length of the homserver name to not cover the whole loginview input with the string.
-  let shortendHomeserverName = Config.defaultServerName()?.slice(0, 25);
+    let shortendHomeserverName = Config.defaultServerName()?.slice(0, 25);
-  shortendHomeserverName =
+    shortendHomeserverName =
-    shortendHomeserverName?.length !== Config.defaultServerName()?.length
+      shortendHomeserverName?.length !== Config.defaultServerName()?.length
-      ? shortendHomeserverName + "..."
+        ? shortendHomeserverName + "..."
-      : shortendHomeserverName;
+        : shortendHomeserverName;
+    node = (
+      <form onSubmit={onSubmitLoginForm}>
+        <FieldRow>
+          <InputField
+            type="text"
+            ref={usernameRef}
+            placeholder={t("common.username")}
+            label={t("common.username")}
+            autoCorrect="off"
+            autoCapitalize="none"
+            prefix="@"
+            suffix={`:${shortendHomeserverName}`}
+            data-testid="login_username"
+          />
+        </FieldRow>
+        <FieldRow>
+          <InputField
+            type="password"
+            ref={passwordRef}
+            placeholder={t("common.password")}
+            label={t("common.password")}
+            data-testid="login_password"
+          />
+        </FieldRow>
+        {error && (
+          <FieldRow>
+            <ErrorMessage error={error} />
+          </FieldRow>
+        )}
+        <FieldRow>
+          <Button
+            type="submit"
+            disabled={loading}
+            data-testid="login_login"
+          >
+            {loading ? t("logging_in") : t("login_title")}
+          </Button>
+        </FieldRow>
+      </form>
+    );
+  } else if (oidcClientConfig !== undefined) {
+    if (!homeserver) {
+      setError(Error("No homeserver is configured"));
+      setLoading(false);
+      return;
+    }
+
+    node = <Button
+      kind="primary"
+      onClick={async () => {
+        // TODO: get the clientId at the same time as doing OIDC discovery
+        const clientId = await getOidcClientId(oidcClientConfig);
+        await startOidcLogin(
+          oidcClientConfig,
+          clientId,
+          homeserver,
+        );
+      }}
+    >
+      {t("room_auth_view_continue_button") /* TODO: make a dedicated word for this */}
+    </Button>;
+  } else {
+    return <LoadingPage />;
+  }
+
   return (
     <>
       <div className={styles.container}>
@@ -89,44 +158,7 @@ export const LoginPage: FC = () => {
 
             <h2>{t("log_in")}</h2>
             <h4>{t("login_subheading")}</h4>
-            <form onSubmit={onSubmitLoginForm}>
+            {node}
-              <FieldRow>
-                <InputField
-                  type="text"
-                  ref={usernameRef}
-                  placeholder={t("common.username")}
-                  label={t("common.username")}
-                  autoCorrect="off"
-                  autoCapitalize="none"
-                  prefix="@"
-                  suffix={`:${shortendHomeserverName}`}
-                  data-testid="login_username"
-                />
-              </FieldRow>
-              <FieldRow>
-                <InputField
-                  type="password"
-                  ref={passwordRef}
-                  placeholder={t("common.password")}
-                  label={t("common.password")}
-                  data-testid="login_password"
-                />
-              </FieldRow>
-              {error && (
-                <FieldRow>
-                  <ErrorMessage error={error} />
-                </FieldRow>
-              )}
-              <FieldRow>
-                <Button
-                  type="submit"
-                  disabled={loading}
-                  data-testid="login_login"
-                >
-                  {loading ? t("logging_in") : t("login_title")}
-                </Button>
-              </FieldRow>
-            </form>
           </div>
           <div className={styles.authLinks}>
             <p>{t("login_auth_links_prompt")}</p>

src/auth/OidcRedirectPage.tsx

@@ -0,0 +1,104 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { useState, type FC } from "react";
+import { useLocation, useNavigate } from "react-router-dom";
+import { useTranslation } from "react-i18next";
+import { createClient, type MatrixClient } from "matrix-js-sdk/src/matrix";
+
+import { useClient } from "../ClientContext";
+import { usePageTitle } from "../usePageTitle";
+import { completeOidcLogin } from "../utils/oidc/authorize";
+import { initClient } from "../utils/matrix";
+
+/**
+ * TODO: Yoinked from element-web, so move to SDK if possible
+ * Gets information about the owner of a given access token.
+ * @returns Promise that resolves with whoami response
+ * @throws when whoami request fails
+ */
+async function getUserIdFromAccessToken(
+  accessToken: string,
+  homeserverUrl: string,
+): Promise<ReturnType<MatrixClient["whoami"]>> {
+  try {
+    const client = createClient({
+      baseUrl: homeserverUrl,
+      accessToken: accessToken,
+    });
+
+    return await client.whoami();
+  } catch (error) {
+    throw new Error("Failed to retrieve userId using accessToken");
+  }
+}
+
+export const OidcRedirectPage: FC = async () => {
+  const { t } = useTranslation();
+  // TODO: probably want a new page title
+  usePageTitle(t("login_title"));
+
+  const navigate = useNavigate();
+  const location = useLocation();
+  const [_, setError] = useState<Error>();
+
+  const { setClient } = useClient();
+  if (!setClient) {
+    return;
+  }
+
+  // TODO: make reactive
+  try {
+    const queryParams = new URLSearchParams(location.search);
+    const { accessToken, refreshToken, homeserverUrl, idToken, clientId, issuer } =
+      await completeOidcLogin(queryParams);
+
+    const {
+      user_id: userId,
+      device_id: deviceId,
+    } = await getUserIdFromAccessToken(accessToken, homeserverUrl);
+
+    const session = {
+      user_id: userId,
+      access_token: accessToken,
+      device_id: deviceId!, // TODO: make sure this really is always defined
+      passwordlessUser: false,
+    };
+
+    console.debug(`TODO: use ${refreshToken}`);
+    const client = await initClient(
+      {
+        baseUrl: homeserverUrl,
+        accessToken,
+        userId,
+        deviceId,
+      },
+      false,
+    );
+    setClient(client, session);
+    console.debug(`TODO: use ${clientId}, ${issuer}, ${idToken}`);
+    // persistOidcAuthenticatedSettings(clientId, issuer, idToken);
+
+    const locationState = location.state;
+    // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+    // @ts-ignore
+    if (locationState && locationState.from) {
+      // eslint-disable-next-line @typescript-eslint/ban-ts-comment
+      // @ts-ignore
+      await navigate(locationState.from);
+    } else {
+      await navigate("/");
+    }
+  } catch (error: any) {
+    setError(error);
+    return;
+  }
+
+  return (
+    <></>
+  );
+}

src/config/ConfigOptions.ts

@@ -1,5 +1,5 @@
 /*
-Copyright 2022-2024 New Vector Ltd.
+Copyright 2022-2025 New Vector Ltd.
 
 SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
@@ -151,6 +151,25 @@ export interface ConfigOptions {
      */
     membership_event_expiry_ms?: number;
   };
+
+  /**
+   * Configuration for OIDC issuers where a static client_id has been issued for the app.
+   * Otherwise dynamic client registration is attempted.
+   */
+  oidc_static_clients?: {
+    [issuer: string]: { client_id: string };
+  };
+
+  oidc_metadata?: {
+    client_name?: string;
+    client_uri?: string;
+    redirect_uris?: string[];
+    logo_uri?: string;
+    application_type?: string;
+    tos_uri?: string;
+    policy_uri?: string;
+    contacts?: string[];
+  }
 }
 
 // Overrides members from ConfigOptions that are always provided by the

src/settings/useSubmitRageshake.test.tsx

@@ -75,6 +75,7 @@ function renderWithMockClient(
     <ClientContextProvider
       value={{
         state: "valid",
+        oidcClientConfig: null,
         disconnected: false,
         supportedFeatures: {
           reactions: true,

src/utils/oidc/authorize.ts

@@ -0,0 +1,96 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { completeAuthorizationCodeGrant, generateOidcAuthorizationUrl } from "matrix-js-sdk/src/oidc/authorize";
+import { OidcClientConfig } from "matrix-js-sdk/src/matrix";
+import { secureRandomString } from "matrix-js-sdk/src/randomstring";
+import { type IdTokenClaims } from "oidc-client-ts";
+
+import { getOidcCallbackUrl } from "./callbackUrl";
+import { OidcClientError } from "./error";
+
+/**
+ * TODO: Mostly yoinked from element-web, so move to SDK if possible
+ * 
+ * Start OIDC authorization code flow
+ * Generates auth params, stores them in session storage and
+ * Navigates to configured authorization endpoint
+ * @param delegatedAuthConfig from discovery
+ * @param clientId this client's id as registered with configured issuer
+ * @param homeserverUrl target homeserver
+ * @returns Promise that resolves after we have navigated to auth endpoint
+ */
+export async function startOidcLogin(
+    delegatedAuthConfig: OidcClientConfig,
+    clientId: string,
+    homeserverUrl: string,
+    isRegistration?: boolean,
+): Promise<void> {
+  const redirectUri = getOidcCallbackUrl().href;
+
+  const nonce = secureRandomString(10);
+
+  const prompt = isRegistration ? "create" : undefined;
+
+  const authorizationUrl = await generateOidcAuthorizationUrl({
+    metadata: delegatedAuthConfig,
+    redirectUri,
+    clientId,
+    homeserverUrl,
+    identityServerUrl: undefined,
+    nonce,
+    prompt,
+  });
+
+  window.location.href = authorizationUrl;
+}
+
+// TODO: Mostly yoinked from element-web, so move to SDK if possible
+type CompleteOidcLoginResponse = {
+  // url of the homeserver selected during login
+  homeserverUrl: string;
+  // accessToken gained from OIDC token issuer
+  accessToken: string;
+  // refreshToken gained from OIDC token issuer, when falsy token cannot be refreshed
+  refreshToken?: string;
+  // idToken gained from OIDC token issuer
+  idToken: string;
+  // this client's id as registered with the OIDC issuer
+  clientId: string;
+  // issuer used during authentication
+  issuer: string;
+  // claims of the given access token; used during token refresh to validate new tokens
+  idTokenClaims: IdTokenClaims;
+};
+
+/**
+ * TODO: Mostly yoinked from element-web, so move to SDK if possible
+ * 
+ * Attempt to complete authorization code flow to get an access token
+ * @param queryParams the query-parameters extracted from the real query-string of the starting URI.
+ * @returns Promise that resolves with a CompleteOidcLoginResponse when login was successful
+ * @throws When we failed to get a valid access token
+ */
+export async function completeOidcLogin(queryParams: URLSearchParams): Promise<CompleteOidcLoginResponse> {
+    const code = queryParams.get("code");
+    const state = queryParams.get("state");
+    if (!code || !state) {
+      throw new Error(OidcClientError.InvalidQueryParameters);
+    }
+    const { homeserverUrl, tokenResponse, idTokenClaims, oidcClientSettings } =
+        await completeAuthorizationCodeGrant(code, state);
+
+    return {
+        homeserverUrl,
+        accessToken: tokenResponse.access_token,
+        refreshToken: tokenResponse.refresh_token,
+        idToken: tokenResponse.id_token,
+        clientId: oidcClientSettings.clientId,
+        issuer: oidcClientSettings.issuer,
+        idTokenClaims,
+    };
+}

src/utils/oidc/callbackUrl.ts

@@ -0,0 +1,14 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/**
+ * The URL to return to after a successful OIDC authentication
+ */
+export function getOidcCallbackUrl(): URL {
+  // TODO: save the path somewhere
+  return new URL("after_login", window.location.origin);
+}

src/utils/oidc/discovery.ts

@@ -0,0 +1,30 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { MatrixClient, MatrixError, OidcClientConfig } from "matrix-js-sdk";
+
+import { Config } from "../../config/Config";
+import { HomeserverMisconfigError } from "../../RichError";
+
+export async function getAuthMetadata(): Promise<OidcClientConfig | null> {
+  const baseUrl = Config.defaultHomeserverUrl(); // TODO: Make this configurable
+  if (!baseUrl) {
+    throw new Error("No homeserver URL configured");
+  }
+  
+  const tempClient = new MatrixClient({ baseUrl });
+  try {
+    return await tempClient.getAuthMetadata();
+  } catch (e) {
+    if (e instanceof MatrixError && e.httpStatus === 404 && e.errcode === "M_UNRECOGNIZED") {
+      // 404 M_UNRECOGNIZED means the server does not support OIDC
+      return null;
+    } else {
+      throw new HomeserverMisconfigError(e instanceof Error ? e.message : undefined);
+    }
+  }
+}

src/utils/oidc/error.ts

@@ -0,0 +1,16 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+/**
+ * TODO: Yoinked from element-web, so move to SDK if possible
+ * 
+ * Errors thrown by EC during OIDC native flow authentication.
+ * Intended to be logged, not read by users.
+ */
+export enum OidcClientError {
+    InvalidQueryParameters = "Invalid query parameters for OIDC native login. `code` and `state` are required.",
+}

src/utils/oidc/isUserRegistrationSupported.ts

@@ -0,0 +1,21 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+// TODO: File yoinked from element-web, so move to SDK if possible
+
+import { type OidcClientConfig } from "matrix-js-sdk/src/matrix";
+
+/**
+ * Check the create prompt is supported by the OP, if so, we can do a registration flow
+ * https://openid.net/specs/openid-connect-prompt-create-1_0.html
+ * @param delegatedAuthConfig config as returned from discovery
+ * @returns whether user registration is supported
+ */
+export function isUserRegistrationSupported(delegatedAuthConfig: OidcClientConfig): boolean {
+    const supportedPrompts = delegatedAuthConfig.prompt_values_supported;
+    return Array.isArray(supportedPrompts) && supportedPrompts?.includes("create");
+}

src/utils/oidc/registerClient.ts

@@ -0,0 +1,61 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { logger } from "matrix-js-sdk/src/logger";
+import { registerOidcClient, type OidcClientConfig } from "matrix-js-sdk";
+
+import { ConfigOptions } from "../../config/ConfigOptions";
+import { Config } from "../../config/Config";
+import { getOidcCallbackUrl } from "./callbackUrl";
+
+/**
+ * TODO: Mostly yoinked from element-web, so move to SDK if possible
+ * 
+ * Get the statically configured clientId for the issuer
+ * @param issuer delegated auth OIDC issuer
+ * @param staticOidcClients static client config from config.json
+ * @returns clientId if found, otherwise undefined
+ */
+function getStaticOidcClientId(
+  issuer: string,
+  staticOidcClients?: ConfigOptions["oidc_static_clients"],
+): string | undefined {
+    // static_oidc_clients are configured with a trailing slash
+    const issuerWithTrailingSlash = issuer.endsWith("/") ? issuer : issuer + "/";
+    return staticOidcClients?.[issuerWithTrailingSlash]?.client_id;
+}
+
+/**
+ * TODO: Mostly yoinked from element-web, so move to SDK if possible
+ * 
+ * Get the statically configured clientId for an OIDC OP
+ * @param delegatedAuthConfig Auth config from OP
+ * @returns resolves with clientId
+ * @throws if no clientId is found
+ */
+export async function getOidcClientId(
+  delegatedAuthConfig: OidcClientConfig,
+): Promise<string> {
+  const config = Config.get();
+  const staticClientId = getStaticOidcClientId(delegatedAuthConfig.issuer, config.oidc_static_clients);
+  if (staticClientId) {
+    logger.debug(`Using static clientId for issuer ${delegatedAuthConfig.issuer}`);
+    return staticClientId;
+  }
+  return await registerOidcClient(
+    delegatedAuthConfig,
+    {
+      clientName: config.oidc_metadata?.client_name ?? "Element Call",
+      clientUri: config.oidc_metadata?.client_uri ?? window.location.origin,
+      redirectUris: [getOidcCallbackUrl().href],
+      applicationType: "web",
+      contacts: config.oidc_metadata?.contacts,
+      tosUri: config.oidc_metadata?.tos_uri,
+      policyUri: config.oidc_metadata?.policy_uri,
+    },
+  );
+}