browser: split browser-check from desktop session check

Split the web browser check from the desktop session checks. In future
commits we will enhance the browser-check to take in to account the WSL
special case.

Author: mjcheetham

src/shared/Core/Authentication/MicrosoftAuthentication.cs

@@ -508,14 +508,14 @@ private void EnsureCanUseEmbeddedWebView()
         private bool CanUseSystemWebView(IPublicClientApplication app, Uri redirectUri)
         {
             // MSAL requires the application redirect URI is a loopback address to use the System WebView
-            return Context.SessionManager.IsDesktopSession && app.IsSystemWebViewAvailable && redirectUri.IsLoopback;
+            return Context.SessionManager.IsWebBrowserAvailable && app.IsSystemWebViewAvailable && redirectUri.IsLoopback;
         }
 
         private void EnsureCanUseSystemWebView(IPublicClientApplication app, Uri redirectUri)
         {
-            if (!Context.SessionManager.IsDesktopSession)
+            if (!Context.SessionManager.IsWebBrowserAvailable)
             {
-                throw new InvalidOperationException("System web view is not available without a desktop session.");
+                throw new InvalidOperationException("System web view is not available without a way to start a browser.");
             }
 
             if (!app.IsSystemWebViewAvailable)

src/shared/Core/BrowserUtils.cs

@@ -28,6 +28,7 @@ public static void OpenDefaultBrowser(IEnvironment environment, Uri uri)
             ProcessStartInfo psi = null;
             if (PlatformUtils.IsLinux())
             {
+                //
                 // On Linux, 'shell execute' utilities like xdg-open launch a process without
                 // detaching from the standard in/out descriptors. Some applications (like
                 // Chromium) write messages to stdout, which is currently hooked up and being

src/shared/Core/EnvironmentBase.cs

@@ -191,5 +191,18 @@ public static string LocateExecutable(this IEnvironment environment, string prog
 
             throw new Exception($"Failed to locate '{program}' executable on the path.");
         }
+
+        /// <summary>
+        /// Retrieves the value of an environment variable from the current process.
+        /// </summary>
+        /// <param name="environment">The <see cref="IEnvironment"/>.</param>
+        /// <param name="variable">The name of the environment variable.</param>
+        /// <returns>
+        /// The value of the environment variable specified by variable, or null if the environment variable is not found.
+        /// </returns>
+        public static string GetEnvironmentVariable(this IEnvironment environment, string variable)
+        {
+            return environment.Variables.TryGetValue(variable, out string value) ? value : null;
+        }
     }
 }

src/shared/Core/ISessionManager.cs

@@ -7,5 +7,18 @@ public interface ISessionManager
         /// </summary>
         /// <returns>True if the session can display UI, false otherwise.</returns>
         bool IsDesktopSession { get; }
+
+        /// <summary>
+        /// Determine if the current session has access to a web browser.
+        /// </summary>
+        /// <returns>True if the session can display a web browser, false otherwise.</returns>
+        bool IsWebBrowserAvailable { get; }
+    }
+    
+    public abstract class SessionManager : ISessionManager
+    {
+        public abstract bool IsDesktopSession { get; }
+
+        public virtual bool IsWebBrowserAvailable => IsDesktopSession;
     }
 }

src/shared/Core/Interop/Posix/PosixSessionManager.cs

@@ -2,15 +2,15 @@
 
 namespace GitCredentialManager.Interop.Posix
 {
-    public class PosixSessionManager : ISessionManager
+    public class PosixSessionManager : SessionManager
     {
         public PosixSessionManager()
         {
             PlatformUtils.EnsurePosix();
         }
 
         // Check if we have an X11 or Wayland display environment available
-        public virtual bool IsDesktopSession =>
+        public override bool IsDesktopSession =>
             !string.IsNullOrWhiteSpace(Environment.GetEnvironmentVariable("DISPLAY")) ||
             !string.IsNullOrWhiteSpace(Environment.GetEnvironmentVariable("WAYLAND_DISPLAY"));
     }

src/shared/Core/Interop/Windows/WindowsSessionManager.cs

@@ -3,14 +3,14 @@
 
 namespace GitCredentialManager.Interop.Windows
 {
-    public class WindowsSessionManager : ISessionManager
+    public class WindowsSessionManager : SessionManager
     {
         public WindowsSessionManager()
         {
             PlatformUtils.EnsureWindows();
         }
 
-        public unsafe bool IsDesktopSession
+        public override unsafe bool IsDesktopSession
         {
             get
             {

src/shared/GitHub/GitHubAuthentication.cs

@@ -64,8 +64,8 @@ public GitHubAuthentication(ICommandContext context)
 
         public async Task<AuthenticationPromptResult> GetAuthenticationAsync(Uri targetUri, string userName, AuthenticationModes modes)
         {
-            // If we don't have a desktop session/GUI then we cannot offer browser
-            if (!Context.SessionManager.IsDesktopSession)
+            // If we cannot start a browser then don't offer the option
+            if (!Context.SessionManager.IsWebBrowserAvailable)
             {
                 modes = modes & ~AuthenticationModes.Browser;
             }
@@ -257,8 +257,8 @@ public async Task<OAuth2TokenResult> GetOAuthTokenViaBrowserAsync(Uri targetUri,
 
             var oauthClient = new GitHubOAuth2Client(HttpClient, Context.Settings, targetUri);
 
-            // We require a desktop session to launch the user's default web browser
-            if (!Context.SessionManager.IsDesktopSession)
+            // Can we launch the user's default web browser?
+            if (!Context.SessionManager.IsWebBrowserAvailable)
             {
                 throw new InvalidOperationException("Browser authentication requires a desktop session");
             }

src/shared/GitLab/GitLabAuthentication.cs

@@ -55,8 +55,8 @@ public GitLabAuthentication(ICommandContext context)
 
         public async Task<AuthenticationPromptResult> GetAuthenticationAsync(Uri targetUri, string userName, AuthenticationModes modes)
         {
-            // If we don't have a desktop session/GUI then we cannot offer browser
-            if (!Context.SessionManager.IsDesktopSession)
+            // If we cannot start a browser then don't offer the option
+            if (!Context.SessionManager.IsWebBrowserAvailable)
             {
                 modes = modes & ~AuthenticationModes.Browser;
             }

src/shared/TestInfrastructure/Objects/TestSessionManager.cs

@@ -3,6 +3,10 @@ namespace GitCredentialManager.Tests.Objects
 {
     public class TestSessionManager : ISessionManager
     {
+        public bool? IsWebBrowserAvailableOverride { get; set; }
+
         public bool IsDesktopSession { get; set; }
+
+        bool ISessionManager.IsWebBrowserAvailable => IsWebBrowserAvailableOverride ?? IsDesktopSession;
     }
 }