pam_get_user - get user name
int pam_get_user(const pam_handle_t *pamh, const char **user, const char *prompt);
The pam_get_user function returns the name of the user specified by pam_start(3). If no user was specified it returns what pam_get_item (pamh, PAM_USER, ... ); would have returned. If this is NULL it obtains the username via the pam_conv(3) mechanism, it prompts the user with the first non-NULL string in the following list:
By whatever means the username is obtained, a pointer to it is returned as the contents of *user. Note, this memory should not be free()'d or modified by the module.