auth: Add mechanism filter for passdbs

src/auth/auth-request.c

@@ -614,6 +614,16 @@ static bool
 auth_request_want_skip_passdb(struct auth_request *request,
 			      struct auth_passdb *passdb)
 {
+	/* if mechanism is not supported, skip */
+	const char *const *mech = passdb->passdb->mechanisms;
+
+	/* if request->mech == NULL it means we are doing
+	   lookup without authentication and should not match this */
+	if (mech != NULL && (request->mech == NULL ||
+	     !str_array_icase_find(mech, request->mech->mech_name))) {
+		return TRUE;
+	}
+
 	/* skip_password_check basically specifies if authentication is
 	   finished */
 	bool authenticated = request->skip_password_check;

src/auth/auth-settings.c

@@ -113,6 +113,7 @@ static const struct setting_define auth_passdb_setting_defines[] = {
 	DEF(SET_STR, args),
 	DEF(SET_STR, default_fields),
 	DEF(SET_STR, override_fields),
+	DEF(SET_STR, mechanisms),
 
 	DEF(SET_ENUM, skip),
 	DEF(SET_ENUM, result_success),
@@ -133,6 +134,7 @@ static const struct auth_passdb_settings auth_passdb_default_settings = {
 	.args = "",
 	.default_fields = "",
 	.override_fields = "",
+	.mechanisms = "",
 
 	.skip = "never:authenticated:unauthenticated",
 	.result_success = "return-ok:return:return-fail:continue:continue-ok:continue-fail",

src/auth/auth-settings.h

@@ -10,6 +10,7 @@ struct auth_passdb_settings {
 	const char *args;
 	const char *default_fields;
 	const char *override_fields;
+	const char *mechanisms;
 
 	const char *skip;
 	const char *result_success;

src/auth/passdb.c

@@ -223,6 +223,13 @@ passdb_preinit(pool_t pool, const struct auth_passdb_settings *set)
 	passdb->id = ++auth_passdb_id;
 	passdb->iface = *iface;
 	passdb->args = p_strdup(pool, set->args);
+	if (*set->mechanisms == '\0') {
+		passdb->mechanisms = NULL;
+	} else if (strcasecmp(set->mechanisms, "none") == 0) {
+		passdb->mechanisms = (const char *const[]){NULL};
+	} else {
+		passdb->mechanisms = (const char* const*)p_strsplit_spaces(pool, set->mechanisms, " ,");
+	}
 
 	array_append(&passdb_modules, &passdb, 1);
 	return passdb;

src/auth/passdb.h

@@ -62,6 +62,9 @@ struct passdb_module {
 	/* Default password scheme for this module.
 	   If cache_key is set, must not be NULL. */
 	const char *default_pass_scheme;
+	/* Supported authentication mechanisms, NULL is all, [NULL] is none*/
+	const char *const *mechanisms;
+
 	/* If blocking is set to TRUE, use child processes to access
 	   this passdb. */
 	bool blocking;