Add support for custom headers in HostedMcpServerTool

src/Libraries/Microsoft.Extensions.AI.Abstractions/Tools/HostedMcpServerTool.cs

@@ -99,4 +99,9 @@ private static string ValidateUrl(Uri serverUrl)
     /// </para>
     /// </remarks>
     public HostedMcpServerToolApprovalMode? ApprovalMode { get; set; }
+
+    /// <summary>
+    /// Gets or sets additional headers to include in requests to the remote MCP server.
+    /// </summary>
+    public IDictionary<string, string>? Headers { get; set; }
 }

src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs

@@ -551,12 +551,12 @@ void IDisposable.Dispose()
                         mcpTool.ServerName,
                         url,
                         mcpTool.AuthorizationToken,
-                        mcpTool.ServerDescription) :
+                        mcpTool.ServerDescription, mcpTool.Headers) :
                     ResponseTool.CreateMcpTool(
                         mcpTool.ServerName,
                         new McpToolConnectorId(mcpTool.ServerAddress),
                         mcpTool.AuthorizationToken,
-                        mcpTool.ServerDescription);
+                        mcpTool.ServerDescription, mcpTool.Headers);
 
                 if (mcpTool.AllowedTools is not null)
                 {

test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Tools/HostedMcpServerToolTests.cs

@@ -65,6 +65,17 @@ public void Constructor_Roundtrips()
         var customApprovalMode = new HostedMcpServerToolRequireSpecificApprovalMode(["tool1"], ["tool2"]);
         tool.ApprovalMode = customApprovalMode;
         Assert.Same(customApprovalMode, tool.ApprovalMode);
+
+        Assert.Null(tool.Headers);
+        IDictionary<string, string> headers = new Dictionary<string, string>
+        {
+            ["X-Custom-Header"] = "value1",
+        };
+        tool.Headers = headers;
+        Assert.Same(headers, tool.Headers);
+
+        tool.Headers = null;
+        Assert.Null(tool.Headers);
     }
 
     [Fact]