Restore OIDC support.

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/MatrixClient.kt

@@ -55,7 +55,12 @@ interface MatrixClient : Closeable {
      * Will close the client and delete the cache data.
      */
     suspend fun clearCache()
-    suspend fun logout()
+
+    /**
+     * Logout the user.
+     * Returns an optional URL. When the URL is there, it should be presented to the user after logout for RP initiated logout on their account page.
+     */
+    suspend fun logout(): String?
     suspend fun loadUserDisplayName(): Result<String>
     suspend fun loadUserAvatarURLString(): Result<String?>
     suspend fun uploadMedia(mimeType: String, data: ByteArray, progressCallback: ProgressCallback?): Result<String>

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/auth/AuthenticationException.kt

@@ -22,6 +22,5 @@ sealed class AuthenticationException(message: String) : Exception(message) {
     class SlidingSyncNotAvailable(message: String) : AuthenticationException(message)
     class SessionMissing(message: String) : AuthenticationException(message)
     class Generic(message: String) : AuthenticationException(message)
-    // TODO Oidc
-    // class OidcError(type: String, message: String) : AuthenticationException(message)
+    data class OidcError(val type: String, override val message: String) : AuthenticationException(message)
 }