Requests a key protection password from the application.
func onKeyPassphraseNeeded(keyID: String, userID: String, mainKey: Bool, passphrase: inout String, skip: inout Bool)
The class fires this event to request a secret key passphrase from the application. Note that this event asks for a key protection passphrase rather than a message protection passphrase. The class fires it when it attempts to use a secret key to sign the data.
This event is fired for every protected secret key residing in SigningKeys. KeyID specifies the key for which the password is requested, and UserID identifies its user. MainKey tells whether the key is a master key or a subkey.
The handler should provide password via the Passphrase parameter, or set Skip to True to skip this key.
For each key KeyPassphraseNeeded is called in a loop until the correct password is provided or the maximum number of password attempts reached.