GSignond API for writing platform adaptation extensions

GSignondExtension — provides platform adaptation functionality
GSignondAccessControlManager — an object that performs access control checks
GSignondSecurityContext — security context descriptor used in access control checks
GSignondStorageManager — manages encrypted disk storage for storing the secret database
GSignondSecretStorage — provides access to the database that stores user credentials and identity/method cache
GSignondCredentials — credentials (username, password) associated with an identity