Called by secret Agents to register their ability to provide and save network secrets. Identifies this agent; only one agent in each user session may use the same identifier. Identifier formatting follows the same rules as D-Bus bus names with the exception that the ':' character is not allowed. The valid set of characters is "[A-Z][a-z][0-9]_-." and the identifier is limited in length to 255 characters with a minimum of 3 characters. An example valid identifier is 'org.gnome.nm-applet' (without quotes). Like Register() but indicates agent capabilities to NetworkManager. See the Register() method's identifier argument. Indicates various agent capabilities to NetworkManager. Called by secret Agents to notify NetworkManager that they will no longer handle requests for network secrets. Agents are automatically unregistered when they disconnect from D-Bus.