Decode a [struct@Value] into [struct@GLib.
Variant] received with the Secret Service DBus API.
The [struct@GLib.Variant] should have a `(oayays)` signature.
A session must have already been established by the [class@Service], and the encoded secret must be valid for that session.
| this |
the service |
| value |
the encoded secret |
|
the decoded secret value |