Re-apply Simon's emebdded e2ee work on latest livekit branch

Replaces https://github.com/vector-im/element-call/pull/1350

src/e2ee/matrixKeyProvider.ts

@@ -0,0 +1,70 @@
+/*
+Copyright 2023 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { BaseKeyProvider, createKeyMaterialFromString } from "livekit-client";
+import { logger } from "matrix-js-sdk/src/logger";
+import {
+  MatrixRTCSession,
+  MatrixRTCSessionEvent,
+} from "matrix-js-sdk/src/matrixrtc/MatrixRTCSession";
+
+export class MatrixKeyProvider extends BaseKeyProvider {
+  private rtcSession?: MatrixRTCSession;
+
+  public setRTCSession(rtcSession: MatrixRTCSession): void {
+    if (this.rtcSession) {
+      this.rtcSession.off(
+        MatrixRTCSessionEvent.EncryptionKeyChanged,
+        this.onEncryptionKeyChanged,
+      );
+    }
+
+    this.rtcSession = rtcSession;
+
+    this.rtcSession.on(
+      MatrixRTCSessionEvent.EncryptionKeyChanged,
+      this.onEncryptionKeyChanged,
+    );
+
+    // The new session could be aware of keys of which the old session wasn't,
+    // so emit a key changed event.
+    for (const [
+      participant,
+      encryptionKeys,
+    ] of this.rtcSession.getEncryptionKeys()) {
+      for (const [index, encryptionKey] of encryptionKeys.entries()) {
+        this.onEncryptionKeyChanged(encryptionKey, index, participant);
+      }
+    }
+  }
+
+  private onEncryptionKeyChanged = async (
+    encryptionKey: string,
+    encryptionKeyIndex: number,
+    participantId: string,
+  ): Promise<void> => {
+    this.onSetEncryptionKey(
+      await createKeyMaterialFromString(encryptionKey),
+      participantId,
+      encryptionKeyIndex,
+    );
+
+    logger.debug(
+      `Embedded-E2EE-LOG onEncryptionKeyChanged participantId=${participantId} encryptionKeyIndex=${encryptionKeyIndex} encryptionKey=${encryptionKey}`,
+      this.getKeys(),
+    );
+  };
+}