authok: add support for Smart Card related authtokens Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

utils: add sss_authtok_[gs]et_2fa Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>

util: Fix const cast failures when building with -Werror When building with -Werror 'make check' fails with many errors like: ../src/tests/cmocka/test_authtok.c: In function ‘test_sss_authtok_password’: ../src/tests/cmocka/test_authtok.c:98:48: error: cast discards ‘__attribute__((const))’ qualifier from pointer target type [-Werror=cast-qual] Make sss_authtok_set() @data argument const, and fix its documentation

Making the authtok structure really opaque. Definition of structure sss_auth_token was removed from header file authtok.h and there left only declaration of this structure. Therefore only way how to use this structure is to use accessory function from same header file. To creating new empty authotok can only be used newly created function sss_authtok_new(). TALLOC context was removed from copy and setter functions, because pointer to stuct sss_auth_token is used as a memory context. All declaration of struct sss_auth_token variables was replaced with pointer to this structure and related changes was made in source code. Function copy_pam_data can copy from argument src which was dynamically allocated with function create_pam_data() or zero initialized struct pam_data allocated on stack. https://fedorahosted.org/sssd/ticket/1830

Add authtok utility functions. These functions allow handling of auth tokens in a completely opaque way, with clear semantics and accessor fucntions that guarantee consistency, proper access to data and error conditions.