Merge pull request #3051 from buildkite/fix-tool-sign-grahql

Allow token to be empty if graphql-token is provided

internal/agenthttp/auth.go

@@ -36,7 +36,7 @@ func (t authenticatedTransport) RoundTrip(req *http.Request) (*http.Response, er
 		}()
 	}
 
-	if t.Token == "" {
+	if t.Token == "" && t.Bearer == "" {
 		return nil, fmt.Errorf("Invalid token, empty string supplied")
 	}