transaction: Add PAM Error types Go definitions

And use them instead of C ones. Given that we have strings for them we
can easily implement error interfaces for it too.

errors.go

@@ -0,0 +1,94 @@
+package pam
+
+/*
+#include <security/pam_appl.h>
+*/
+import "C"
+
+// Error is the Type for PAM Return types
+type Error int
+
+// Pam Return types
+const (
+	// OpenErr indicates a dlopen() failure when dynamically loading a
+	// service module.
+	ErrOpen Error = C.PAM_OPEN_ERR
+	// ErrSymbol indicates a symbol not found.
+	ErrSymbol Error = C.PAM_SYMBOL_ERR
+	// ErrService indicates a error in service module.
+	ErrService Error = C.PAM_SERVICE_ERR
+	// ErrSystem indicates a system error.
+	ErrSystem Error = C.PAM_SYSTEM_ERR
+	// ErrBuf indicates a memory buffer error.
+	ErrBuf Error = C.PAM_BUF_ERR
+	// ErrPermDenied indicates a permission denied.
+	ErrPermDenied Error = C.PAM_PERM_DENIED
+	// ErrAuth indicates a authentication failure.
+	ErrAuth Error = C.PAM_AUTH_ERR
+	// ErrCredInsufficient indicates a can not access authentication data due to
+	// insufficient credentials.
+	ErrCredInsufficient Error = C.PAM_CRED_INSUFFICIENT
+	// ErrAuthinfoUnavail indicates that the underlying authentication service
+	// can not retrieve authentication information.
+	ErrAuthinfoUnavail Error = C.PAM_AUTHINFO_UNAVAIL
+	// ErrUserUnknown indicates a user not known to the underlying authentication
+	// module.
+	ErrUserUnknown Error = C.PAM_USER_UNKNOWN
+	// ErrMaxtries indicates that an authentication service has maintained a retry
+	// count which has been reached. No further retries should be attempted.
+	ErrMaxtries Error = C.PAM_MAXTRIES
+	// ErrNewAuthtokReqd indicates a new authentication token required. This is
+	// normally returned if the machine security policies require that the
+	// password should be changed because the password is nil or it has aged.
+	ErrNewAuthtokReqd Error = C.PAM_NEW_AUTHTOK_REQD
+	// ErrAcctExpired indicates that an user account has expired.
+	ErrAcctExpired Error = C.PAM_ACCT_EXPIRED
+	// ErrSession indicates a can not make/remove an entry for the
+	// specified session.
+	ErrSession Error = C.PAM_SESSION_ERR
+	// ErrCredUnavail indicates that an underlying authentication service can not
+	// retrieve user credentials.
+	ErrCredUnavail Error = C.PAM_CRED_UNAVAIL
+	// ErrCredExpired indicates that an user credentials expired.
+	ErrCredExpired Error = C.PAM_CRED_EXPIRED
+	// ErrCred indicates a failure setting user credentials.
+	ErrCred Error = C.PAM_CRED_ERR
+	// ErrNoModuleData indicates a no module specific data is present.
+	ErrNoModuleData Error = C.PAM_NO_MODULE_DATA
+	// ErrConv indicates a conversation error.
+	ErrConv Error = C.PAM_CONV_ERR
+	// ErrAuthtokErr indicates an authentication token manipulation error.
+	ErrAuthtok Error = C.PAM_AUTHTOK_ERR
+	// ErrAuthtokRecoveryErr indicates an authentication information cannot
+	// be recovered.
+	ErrAuthtokRecovery Error = C.PAM_AUTHTOK_RECOVERY_ERR
+	// ErrAuthtokLockBusy indicates am authentication token lock busy.
+	ErrAuthtokLockBusy Error = C.PAM_AUTHTOK_LOCK_BUSY
+	// ErrAuthtokDisableAging indicates an authentication token aging disabled.
+	ErrAuthtokDisableAging Error = C.PAM_AUTHTOK_DISABLE_AGING
+	// ErrTryAgain indicates a preliminary check by password service.
+	ErrTryAgain Error = C.PAM_TRY_AGAIN
+	// ErrIgnore indicates to ignore underlying account module regardless of
+	// whether the control flag is required, optional, or sufficient.
+	ErrIgnore Error = C.PAM_IGNORE
+	// ErrAbort indicates a critical error (module fail now request).
+	ErrAbort Error = C.PAM_ABORT
+	// ErrAuthtokExpired indicates an user's authentication token has expired.
+	ErrAuthtokExpired Error = C.PAM_AUTHTOK_EXPIRED
+	// ErrModuleUnknown indicates a module is not known.
+	ErrModuleUnknown Error = C.PAM_MODULE_UNKNOWN
+	// ErrBadItem indicates a bad item passed to pam_*_item().
+	ErrBadItem Error = C.PAM_BAD_ITEM
+	// ErrConvAgain indicates a conversation function is event driven and data
+	// is not available yet.
+	ErrConvAgain Error = C.PAM_CONV_AGAIN
+	// ErrIncomplete indicates to please call this function again to complete
+	// authentication stack. Before calling again, verify that conversation
+	// is completed.
+	ErrIncomplete Error = C.PAM_INCOMPLETE
+)
+
+// Error returns the error message for the given status.
+func (status Error) Error() string {
+	return C.GoString(C.pam_strerror(nil, C.int(status)))
+}