gh cli auth (#534)

* call the gh auth token for non azure pipelines workloads
* prepend this github_token
* fix setting values to empty string, e.g. `-s github_token=` to unset

src/Runner.Client/GhCliAuth.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using GitHub.Runner.Sdk;
+
+namespace Runner.Client
+{
+    public class GhCliAuth {
+        public static async Task<string> GetToken(string workingDirectory, ITraceWriter trace, CancellationToken token) {
+            string line = null;
+            void handleOutput(object s, ProcessDataReceivedEventArgs e)
+            {
+                line ??= e.Data;
+            }
+            try {
+                var gh = WhichUtil.Which("gh", require: false, trace: trace);
+                if (string.IsNullOrWhiteSpace(gh))
+                {
+                    return null;
+                }
+                var ghInvoker = new ProcessInvoker(trace);
+                ghInvoker.OutputDataReceived += handleOutput;
+                await ghInvoker.ExecuteAsync(workingDirectory, gh, "auth token", new Dictionary<string, string>(), token);
+                return line;
+            } catch {
+                return null;
+            }
+        }
+    }
+}

src/Runner.Client/Program.cs

@@ -2002,6 +2002,12 @@ await Task.WhenAny(Task.Run(() => {
                                             }
                                         }
                                     }
+                                    if(parameters.Event != "azpipelines") {
+                                        var githubToken = await GhCliAuth.GetToken(null, new TraceWriter(parameters), CancellationToken.None);
+                                        if(githubToken != null) {
+                                            wsecrets.Add($"github_token={githubToken}");
+                                        }
+                                    }
                                     if(parameters.Secrets?.Length > 0) {
                                         for(int i = 0; i < parameters.Secrets.Length; i++ ) {
                                             var e = parameters.Secrets[i];

src/Runner.Server/Controllers/MessageController.cs

@@ -389,7 +389,7 @@ private static void LoadEnvSec(string[] contents, Action<string, string> kvhandl
                     if (separatorIndex > 0)
                     {
                         string envKey = env.Substring(0, separatorIndex);
-                        string envValue = null;
+                        string envValue = "";
                         if (env.Length > separatorIndex + 1)
                         {
                             envValue = env.Substring(separatorIndex + 1);