Determines whether the credential value has been securely cleared.
true if the credential has been cleared, otherwise false.
default void clear()
Clears the credential. For example, if the credential includes a password,
this method would overwrite the password value.
default boolean isValid()
Determines whether the credential is valid. This would be called as part of
the credential validation process to check the integrity of the credential,
such as a signature check. This check would be self-contained,
not requiring identity store access.