fix: Do not overwrite user ip if set manually in ASP.NET sdk (#4513)

Author: alexsohn1126

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### Fixes
+
+- Do not overwrite user IP if it is set manually in ASP.NET sdk ([#4513](https://github.com/getsentry/sentry-dotnet/pull/4513))
+
 ## 5.15.0
 
 ### Features

src/Sentry.AspNet/Internal/SystemWebRequestEventProcessor.cs

@@ -73,7 +73,7 @@ public SystemWebRequestEventProcessor(IRequestPayloadExtractor payloadExtractor,
                 @event.User.Username = null;
             }
 
-            @event.User.IpAddress = context.Request.UserHostAddress;
+            @event.User.IpAddress ??= context.Request.UserHostAddress;
             if (context.User.Identity is { } identity)
             {
                 @event.User.Username = identity.Name;

test/Sentry.AspNet.Tests/Internal/SystemWebRequestEventProcessorTests.cs

@@ -70,4 +70,21 @@ public void Process_NoBodyExtracted_NoRequestData()
         Assert.Same(expected, actual);
         Assert.Null(expected.Request.Data);
     }
+
+    [Fact]
+    public void Process_PresetUserIP_NotOverwritten()
+    {
+        const string userIp = "192.0.0.1";
+        var evt = new SentryEvent();
+        evt.User.IpAddress = userIp;
+
+        Context = HttpContextBuilder.Build();
+        // Ensure user is not null
+        Context.User = new GenericPrincipal(new GenericIdentity("TestUser"), null);
+        _fixture.SentryOptions.SendDefaultPii = true;
+        var sut = _fixture.GetSut();
+
+        var processedEvt = sut.Process(evt);
+        Assert.Equal(userIp, processedEvt?.User.IpAddress);
+    }
 }