Adapt OAuth2 implementation to Matrix Spec v1.18 (#34026)

* Adapt OAuth2 implementation to Matrix Spec v1.18

* Handle more cases of oidc->oauth

* Fix test

* Fix read back of oauth2 context

* Iterate

* Fix tests

* Discard changes to apps/web/playwright/e2e/settings/account-user-settings-tab.spec.ts

* Fix test

* Fix test

* Fix test

* Potential fix for pull request finding 'Unused variable, import, function or class'

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

* Iterate

* Iterate

* Fix test

---------

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apps/web/test/unit-tests/components/views/dialogs/UserSettingsDialog-test.tsx

@@ -28,7 +28,7 @@ import { UIFeature } from "../../../../../src/settings/UIFeature";
 import { SettingLevel } from "../../../../../src/settings/SettingLevel";
 import { TestSDKContext } from "../../../TestSDKContext.ts";
 import { type FeatureSettingKey } from "../../../../../src/settings/Settings.tsx";
-import { mockOpenIdConfiguration } from "../../../../test-utils/oidc.ts";
+import { makeDelegatedAuthMetadata } from "../../../../test-utils/auth.ts";
 
 mockPlatformPeg({
     supportsSpellCheckSettings: jest.fn().mockReturnValue(false),
@@ -74,7 +74,7 @@ describe("<UserSettingsDialog />", () => {
             getPushers: jest.fn().mockResolvedValue([]),
             getProfileInfo: jest.fn().mockResolvedValue({}),
             getMediaConfig: jest.fn(),
-            getAuthMetadata: jest.fn().mockResolvedValue(mockOpenIdConfiguration()),
+            getAuthMetadata: jest.fn().mockResolvedValue(makeDelegatedAuthMetadata()),
         });
         sdkContext = new TestSDKContext();
         sdkContext._client = mockClient;