Remove the `.Provider.` bit.
diff --git a/openstack/identity/v3/tokens/requests.go b/openstack/identity/v3/tokens/requests.go
index dfef0ce..d8d74fb 100644
--- a/openstack/identity/v3/tokens/requests.go
+++ b/openstack/identity/v3/tokens/requests.go
@@ -14,7 +14,7 @@
 }
 
 func subjectTokenHeaders(c *gophercloud.ServiceClient, subjectToken string) map[string]string {
-	h := c.Provider.AuthenticatedHeaders()
+	h := c.AuthenticatedHeaders()
 	h["X-Subject-Token"] = subjectToken
 	return h
 }