core: add credentials logic

Fixes: #15778 #16060

src/basic/path-util.c

@@ -14,6 +14,7 @@
 
 #include "alloc-util.h"
 #include "extract-word.h"
+#include "fd-util.h"
 #include "fs-util.h"
 #include "glob-util.h"
 #include "log.h"
@@ -1127,3 +1128,9 @@ bool prefixed_path_strv_contains(char **l, const char *path) {
 
         return false;
 }
+
+bool credential_name_valid(const char *s) {
+        /* We want that credential names are both valid in filenames (since that's our primary way to pass
+         * them around) and as fdnames (which is how we might want to pass them around eventually) */
+        return filename_is_valid(s) && fdname_is_valid(s);
+}