diff --git a/.gitignore b/.gitignore
index 694735b6..4e004036 100644
--- a/.gitignore
+++ b/.gitignore
@@ -131,5 +131,9 @@ out
 .yarn/install-state.gz
 .pnp.*
 
+# IDE
+.vscode/
+.idea/
+
 .DS_Store
 dist/
diff --git a/src/client/sse.test.ts b/src/client/sse.test.ts
index 4fce9976..bf9accbe 100644
--- a/src/client/sse.test.ts
+++ b/src/client/sse.test.ts
@@ -13,8 +13,21 @@ describe("SSEClientTransport", () => {
   let resourceBaseUrl: URL;
   let authBaseUrl: URL;
   let lastServerRequest: IncomingMessage;
+  const serverRequests: Record<string, IncomingMessage[]> = {};
   let sendServerMessage: ((message: string) => void) | null = null;
 
+  const recordServerRequest = (req: IncomingMessage, res: ServerResponse) => {
+    lastServerRequest = req;
+
+    const key = `${req.method} ${req.url}`;
+    serverRequests[key] = serverRequests[key] || [];
+    serverRequests[key].push(req);
+
+    res.on('finish', () => {
+      console.log(`[server] ${req.method} ${req.url} -> ${res.statusCode} ${res.statusMessage}`);
+    });
+  };
+
   beforeEach((done) => {
     // Reset state
     lastServerRequest = null as unknown as IncomingMessage;
@@ -613,6 +626,8 @@ describe("SSEClientTransport", () => {
       authServer.close();
 
       authServer = createServer((req, res) => {
+        recordServerRequest(req, res);
+
         if (req.url && authServerMetadataUrls.includes(req.url)) {
           res.writeHead(404).end();
           return;
@@ -625,7 +640,7 @@ describe("SSEClientTransport", () => {
           req.on("end", () => {
             const params = new URLSearchParams(body);
             if (params.get("grant_type") === "refresh_token" &&
-              params.get("refresh_token") === "refresh-token" &&
+              params.get("refresh_token")?.includes("refresh-token") &&
               params.get("client_id") === "test-client-id" &&
               params.get("client_secret") === "test-client-secret") {
               res.writeHead(200, { "Content-Type": "application/json" });
@@ -656,6 +671,7 @@ describe("SSEClientTransport", () => {
 
       let connectionAttempts = 0;
       resourceServer = createServer((req, res) => {
+        recordServerRequest(req, res);
         lastServerRequest = req;
 
         if (req.url === "/.well-known/oauth-protected-resource") {
@@ -705,6 +721,14 @@ describe("SSEClientTransport", () => {
 
       transport = new SSEClientTransport(resourceBaseUrl, {
         authProvider: mockAuthProvider,
+        eventSourceInit: {
+          fetch: (url, init) => {
+            return fetch(url, { ...init, headers: {
+              ...(init?.headers instanceof Headers ? Object.fromEntries(init.headers.entries()) : init?.headers),
+              'X-Custom-Header': 'custom-value'
+            } });
+          }
+        },
       });
 
       await transport.start();
@@ -716,6 +740,9 @@ describe("SSEClientTransport", () => {
       });
       expect(connectionAttempts).toBe(1);
       expect(lastServerRequest.headers.authorization).toBe("Bearer new-token");
+      expect(serverRequests["GET /"]).toHaveLength(2);
+      expect(serverRequests["GET /"]
+        .every(req => req.headers["x-custom-header"] === "custom-value")).toBe(true);
     });
 
     it("refreshes expired token during POST request", async () => {
@@ -1145,11 +1172,11 @@ describe("SSEClientTransport", () => {
 
       return {
         get redirectUrl() { return "http://localhost/callback"; },
-        get clientMetadata() { 
-          return { 
+        get clientMetadata() {
+          return {
             redirect_uris: ["http://localhost/callback"],
             client_name: "Test Client"
-          }; 
+          };
         },
         clientInformation: jest.fn().mockResolvedValue(clientInfo),
         tokens: jest.fn().mockResolvedValue(tokens),
@@ -1175,7 +1202,7 @@ describe("SSEClientTransport", () => {
           }));
           return;
         }
-  
+
         if (req.url === "/token" && req.method === "POST") {
           // Handle token exchange request
           let body = "";
@@ -1198,7 +1225,7 @@ describe("SSEClientTransport", () => {
           });
           return;
         }
-  
+
         res.writeHead(404).end();
       });
 
@@ -1302,14 +1329,14 @@ describe("SSEClientTransport", () => {
 
       // Verify custom fetch was used
       expect(customFetch).toHaveBeenCalled();
-      
+
       // Verify specific OAuth endpoints were called with custom fetch
       const customFetchCalls = customFetch.mock.calls;
       const callUrls = customFetchCalls.map(([url]) => url.toString());
-      
+
       // Should have called resource metadata discovery
       expect(callUrls.some(url => url.includes('/.well-known/oauth-protected-resource'))).toBe(true);
-      
+
       // Should have called OAuth authorization server metadata discovery
       expect(callUrls.some(url => url.includes('/.well-known/oauth-authorization-server'))).toBe(true);
 
@@ -1375,19 +1402,19 @@ describe("SSEClientTransport", () => {
 
       // Verify custom fetch was used
       expect(customFetch).toHaveBeenCalled();
-      
+
       // Verify specific OAuth endpoints were called with custom fetch
       const customFetchCalls = customFetch.mock.calls;
       const callUrls = customFetchCalls.map(([url]) => url.toString());
-      
+
       // Should have called resource metadata discovery
       expect(callUrls.some(url => url.includes('/.well-known/oauth-protected-resource'))).toBe(true);
-      
+
       // Should have called OAuth authorization server metadata discovery
       expect(callUrls.some(url => url.includes('/.well-known/oauth-authorization-server'))).toBe(true);
 
       // Should have attempted the POST request that triggered the 401
-      const postCalls = customFetchCalls.filter(([url, options]) => 
+      const postCalls = customFetchCalls.filter(([url, options]) =>
         url.toString() === resourceBaseUrl.href && options?.method === "POST"
       );
       expect(postCalls.length).toBeGreaterThan(0);
@@ -1417,19 +1444,19 @@ describe("SSEClientTransport", () => {
 
       // Verify custom fetch was used
       expect(customFetch).toHaveBeenCalled();
-      
+
       // Verify specific OAuth endpoints were called with custom fetch
       const customFetchCalls = customFetch.mock.calls;
       const callUrls = customFetchCalls.map(([url]) => url.toString());
-      
+
       // Should have called resource metadata discovery
       expect(callUrls.some(url => url.includes('/.well-known/oauth-protected-resource'))).toBe(true);
-      
+
       // Should have called OAuth authorization server metadata discovery
       expect(callUrls.some(url => url.includes('/.well-known/oauth-authorization-server'))).toBe(true);
 
       // Should have called token endpoint for authorization code exchange
-      const tokenCalls = customFetchCalls.filter(([url, options]) => 
+      const tokenCalls = customFetchCalls.filter(([url, options]) =>
         url.toString().includes('/token') && options?.method === "POST"
       );
       expect(tokenCalls.length).toBeGreaterThan(0);
diff --git a/src/client/sse.ts b/src/client/sse.ts
index e1c86ccd..deffeaba 100644
--- a/src/client/sse.ts
+++ b/src/client/sse.ts
@@ -35,11 +35,6 @@ export type SSEClientTransportOptions = {
 
   /**
    * Customizes the initial SSE request to the server (the request that begins the stream).
-   *
-   * NOTE: Setting this property will prevent an `Authorization` header from
-   * being automatically attached to the SSE request, if an `authProvider` is
-   * also given. This can be worked around by setting the `Authorization` header
-   * manually.
    */
   eventSourceInit?: EventSourceInit;