skip "tagged-devices" in userExists check

Currently, the special "tagged-devices" user (which exists for any
tagged devices in the tailnet) can own go links.  This change permits
tagged devices to continue to create go links, but skips over them for
ownership checks, allowing any human user can take over ownership.

Fixes #37

Signed-off-by: Will Norris <[email protected]>

Author: willnorris

golink.go

@@ -457,6 +457,8 @@ func currentUser(r *http.Request) (string, error) {
 
 // userExists returns whether a user exists with the specified login in the current tailnet.
 func userExists(ctx context.Context, login string) (bool, error) {
+	const userTaggedDevices = "tagged-devices" // owner of tagged devices
+
 	if devMode() {
 		// in dev mode, just assume the user exists
 		return true, nil
@@ -466,6 +468,9 @@ func userExists(ctx context.Context, login string) (bool, error) {
 		return false, err
 	}
 	for _, user := range st.User {
+		if user.LoginName == userTaggedDevices {
+			continue
+		}
 		if user.LoginName == login {
 			return true, nil
 		}