Add copy media backup id to backup playground.

app/src/main/java/org/thoughtcrime/securesms/components/settings/app/internal/backup/InternalBackupPlaygroundFragment.kt

@@ -77,6 +77,7 @@ import org.signal.core.ui.compose.Rows
 import org.signal.core.ui.compose.SignalPreview
 import org.signal.core.ui.compose.Snackbars
 import org.signal.core.ui.compose.TextFields.TextField
+import org.signal.core.util.Base64
 import org.signal.core.util.Hex
 import org.signal.core.util.getLength
 import org.thoughtcrime.securesms.R
@@ -462,6 +463,15 @@ fun Screen(
         }
       )
 
+      Rows.TextRow(
+        text = "Copy Media Backup ID",
+        label = "Copies the Media Backup ID, Base64 encoded; it can be used to identify your media backup on the server.",
+        onClick = {
+          Util.copyToClipboard(context, Base64.encodeWithoutPadding(SignalStore.backup.mediaRootBackupKey.deriveBackupId(SignalStore.account.requireAci()).value))
+          Toast.makeText(context, "Copied!", Toast.LENGTH_SHORT).show()
+        }
+      )
+
       Dividers.Default()
 
       Text(

libsignal-service/src/main/java/org/whispersystems/signalservice/api/backup/MediaRootBackupKey.kt

@@ -51,6 +51,15 @@ class MediaRootBackupKey(override val value: ByteArray) : BackupKey {
     )
   }
 
+  /**
+   * Identifies a the location of a user's backup.
+   */
+  fun deriveBackupId(aci: ACI): BackupId {
+    return BackupId(
+      LibSignalBackupKey(value).deriveBackupId(aci.libSignalAci)
+    )
+  }
+
   class MediaKeyMaterial(
     val id: MediaId,
     val macKey: ByteArray,