read GH_OAUTH_PORT from the environmnent to listen on a predictable port

webapp/local_server.go

@@ -13,10 +13,9 @@ type CodeResponse struct {
 	Code  string
 	State string
 }
-
-// bindLocalServer initializes a LocalServer that will listen on a randomly available TCP port.
-func bindLocalServer() (*localServer, error) {
-	listener, err := net.Listen("tcp4", "127.0.0.1:0")
+func bindLocalServerWithPort(port int) (*localServer, error) {
+	addr := fmt.Sprintf("127.0.0.1:%d", port)
+	listener, err := net.Listen("tcp4", addr)
 	if err != nil {
 		return nil, err
 	}
@@ -27,6 +26,12 @@ func bindLocalServer() (*localServer, error) {
 	}, nil
 }
 
+// bindLocalServer initializes a LocalServer that will listen on a randomly available TCP port.
+func bindLocalServer() (*localServer, error) {
+	return bindLocalServerWithPort(0)
+
+}
+
 type localServer struct {
 	CallbackPath     string
 	WriteSuccessHTML func(w io.Writer)

webapp/webapp_flow.go

@@ -11,8 +11,9 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"os"
 	"strings"
-
+	"strconv"
 	"github.com/cli/oauth/api"
 )
 
@@ -29,7 +30,20 @@ type Flow struct {
 
 // InitFlow creates a new Flow instance by detecting a locally available port number.
 func InitFlow() (*Flow, error) {
-	server, err := bindLocalServer()
+
+	portStr := os.Getenv("GH_OAUTH_PORT")
+	port := 0
+
+
+	if portStr != "" {
+		var err error
+		port, err = strconv.Atoi(portStr)
+		if err != nil {
+			port = 0
+		}
+	}
+
+	server, err := bindLocalServerWithPort(port)
 	if err != nil {
 		return nil, err
 	}