From f695c4db040f84e54a28aa04c0e9bff2ded8cc9a Mon Sep 17 00:00:00 2001
From: Simon Rozsival <simon@rozsival.com>
Date: Tue, 15 Sep 2026 12:53:55 +0200
Subject: [PATCH] [net] Make authentication modules trimmable

Delay creation of the built-in Basic and Digest authentication modules until PreAuthenticationData is configured, allowing unused implementations to be removed by the linker.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
---
 .../AndroidMessageHandler.cs                  | 23 +++++++++++++------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/Mono.Android/Xamarin.Android.Net/AndroidMessageHandler.cs b/src/Mono.Android/Xamarin.Android.Net/AndroidMessageHandler.cs
index b2eb1d0eae6..94a34ad15b9 100644
--- a/src/Mono.Android/Xamarin.Android.Net/AndroidMessageHandler.cs
+++ b/src/Mono.Android/Xamarin.Android.Net/AndroidMessageHandler.cs
@@ -507,13 +507,9 @@ or ObjectDisposedException
 			"Last-Modified"
 		};
 
-		static readonly List <IAndroidAuthenticationModule> authModules = new List <IAndroidAuthenticationModule> {
-			new AuthModuleBasic (),
-			new AuthModuleDigest ()
-		};
-
 		CookieContainer? _cookieContainer;
 		DecompressionMethods _decompressionMethods;
+		IAndroidAuthenticationModule []? authModules;
 
 		bool disposed;
 		bool started;
@@ -759,7 +755,20 @@ public int MaxAutomaticRedirections
 		/// </para>
 		/// </summary>
 		/// <value>The pre authentication data.</value>
-		public AuthenticationData? PreAuthenticationData { get; set; }
+		public AuthenticationData? PreAuthenticationData {
+			get;
+			set {
+				// Keep these constructor references in the setter so apps that never configure pre-authentication can trim the built-in modules.
+				if (value != null && authModules == null) {
+					authModules = [
+						new AuthModuleBasic (),
+						new AuthModuleDigest ()
+					];
+				}
+
+				field = value;
+			}
+		}
 
 		/// <summary>
 		/// If the website requires authentication, this property will contain data about each scheme supported
@@ -1768,7 +1777,7 @@ void HandlePreAuthentication (HttpURLConnection httpConnection)
 				return;
 			}
 
-			var auth = data.Scheme == AuthenticationScheme.Unsupported ? data.AuthModule : authModules.Find (m => m?.Scheme == data.Scheme);
+			var auth = data.Scheme == AuthenticationScheme.Unsupported ? data.AuthModule : authModules?.FirstOrDefault (m => m.Scheme == data.Scheme);
 			if (auth == null) {
 				if (Logger.LogNet)
 					Logger.Log (LogLevel.Info, LOG_APP, $"Authentication module for scheme '{data.Scheme}' not found. No authentication will be performed");