diff --git a/src/server/auth/proxyProvider.test.ts b/src/server/auth/proxyProvider.test.ts
new file mode 100644
index 00000000..9a0ae3da
--- /dev/null
+++ b/src/server/auth/proxyProvider.test.ts
@@ -0,0 +1,285 @@
+import { Response } from "express";
+import { ProxyOAuthServerProvider, ProxyOptions } from "./proxyProvider.js";
+import { AuthInfo } from "./types.js";
+import { OAuthClientInformationFull, OAuthTokens } from "../../shared/auth.js";
+import { ServerError } from "./errors.js";
+
+describe("Proxy OAuth Server Provider", () => {
+  // Mock client data
+  const validClient: OAuthClientInformationFull = {
+    client_id: "test-client",
+    client_secret: "test-secret",
+    redirect_uris: ["https://example.com/callback"],
+  };
+
+  // Mock response object
+  const mockResponse = {
+    redirect: jest.fn(),
+  } as unknown as Response;
+
+  // Base provider options
+  const baseOptions: ProxyOptions = {
+    endpoints: {
+      authorizationUrl: "https://auth.example.com/authorize",
+      tokenUrl: "https://auth.example.com/token",
+      revocationUrl: "https://auth.example.com/revoke",
+      registrationUrl: "https://auth.example.com/register",
+    },
+    verifyToken: jest.fn().mockImplementation(async (token: string) => {
+      if (token === "valid-token") {
+        return {
+          token,
+          clientId: "test-client",
+          scopes: ["read", "write"],
+          expiresAt: Date.now() / 1000 + 3600,
+        } as AuthInfo;
+      }
+      throw new Error("Invalid token");
+    }),
+    getClient: jest.fn().mockImplementation(async (clientId: string) => {
+      if (clientId === "test-client") {
+        return validClient;
+      }
+      return undefined;
+    }),
+  };
+
+  let provider: ProxyOAuthServerProvider;
+  let originalFetch: typeof global.fetch;
+
+  beforeEach(() => {
+    provider = new ProxyOAuthServerProvider(baseOptions);
+    originalFetch = global.fetch;
+    global.fetch = jest.fn();
+  });
+
+  afterEach(() => {
+    global.fetch = originalFetch;
+    jest.clearAllMocks();
+  });
+
+  describe("authorization", () => {
+    it("redirects to authorization endpoint with correct parameters", async () => {
+      await provider.authorize(
+        validClient,
+        {
+          redirectUri: "https://example.com/callback",
+          codeChallenge: "test-challenge",
+          state: "test-state",
+          scopes: ["read", "write"],
+        },
+        mockResponse
+      );
+
+      const expectedUrl = new URL("https://auth.example.com/authorize");
+      expectedUrl.searchParams.set("client_id", "test-client");
+      expectedUrl.searchParams.set("response_type", "code");
+      expectedUrl.searchParams.set("redirect_uri", "https://example.com/callback");
+      expectedUrl.searchParams.set("code_challenge", "test-challenge");
+      expectedUrl.searchParams.set("code_challenge_method", "S256");
+      expectedUrl.searchParams.set("state", "test-state");
+      expectedUrl.searchParams.set("scope", "read write");
+
+      expect(mockResponse.redirect).toHaveBeenCalledWith(expectedUrl.toString());
+    });
+
+    it("throws error when authorization endpoint is not configured", async () => {
+      const providerWithoutAuth = new ProxyOAuthServerProvider({
+        ...baseOptions,
+        endpoints: { ...baseOptions.endpoints, authorizationUrl: undefined },
+      });
+
+      await expect(
+        providerWithoutAuth.authorize(validClient, {
+          redirectUri: "https://example.com/callback",
+          codeChallenge: "test-challenge",
+        }, mockResponse)
+      ).rejects.toThrow("No authorization endpoint configured");
+    });
+  });
+
+  describe("token exchange", () => {
+    const mockTokenResponse: OAuthTokens = {
+      access_token: "new-access-token",
+      token_type: "Bearer",
+      expires_in: 3600,
+      refresh_token: "new-refresh-token",
+    };
+
+    beforeEach(() => {
+      (global.fetch as jest.Mock).mockImplementation(() => 
+        Promise.resolve({
+          ok: true,
+          json: () => Promise.resolve(mockTokenResponse),
+        })
+      );
+    });
+
+    it("exchanges authorization code for tokens", async () => {
+      const tokens = await provider.exchangeAuthorizationCode(
+        validClient,
+        "test-code",
+        "test-verifier"
+      );
+
+      expect(global.fetch).toHaveBeenCalledWith(
+        "https://auth.example.com/token",
+        expect.objectContaining({
+          method: "POST",
+          headers: {
+            "Content-Type": "application/x-www-form-urlencoded",
+          },
+          body: expect.stringContaining("grant_type=authorization_code")
+        })
+      );
+      expect(tokens).toEqual(mockTokenResponse);
+    });
+
+    it("exchanges refresh token for new tokens", async () => {
+      const tokens = await provider.exchangeRefreshToken(
+        validClient,
+        "test-refresh-token",
+        ["read", "write"]
+      );
+
+      expect(global.fetch).toHaveBeenCalledWith(
+        "https://auth.example.com/token",
+        expect.objectContaining({
+          method: "POST",
+          headers: {
+            "Content-Type": "application/x-www-form-urlencoded",
+          },
+          body: expect.stringContaining("grant_type=refresh_token")
+        })
+      );
+      expect(tokens).toEqual(mockTokenResponse);
+    });
+
+    it("throws error when token endpoint is not configured", async () => {
+      const providerWithoutToken = new ProxyOAuthServerProvider({
+        ...baseOptions,
+        endpoints: { ...baseOptions.endpoints, tokenUrl: undefined },
+      });
+
+      await expect(
+        providerWithoutToken.exchangeAuthorizationCode(validClient, "test-code")
+      ).rejects.toThrow("No token endpoint configured");
+    });
+
+    it("handles token exchange failure", async () => {
+      (global.fetch as jest.Mock).mockImplementation(() => 
+        Promise.resolve({
+          ok: false,
+          status: 400,
+        })
+      );
+
+      await expect(
+        provider.exchangeAuthorizationCode(validClient, "invalid-code")
+      ).rejects.toThrow(ServerError);
+    });
+  });
+
+  describe("client registration", () => {
+    it("registers new client", async () => {
+      const newClient: OAuthClientInformationFull = {
+        client_id: "new-client",
+        redirect_uris: ["https://new-client.com/callback"],
+      };
+
+      (global.fetch as jest.Mock).mockImplementation(() => 
+        Promise.resolve({
+          ok: true,
+          json: () => Promise.resolve(newClient),
+        })
+      );
+
+      const result = await provider.clientsStore.registerClient!(newClient);
+
+      expect(global.fetch).toHaveBeenCalledWith(
+        "https://auth.example.com/register",
+        expect.objectContaining({
+          method: "POST",
+          headers: {
+            "Content-Type": "application/json",
+          },
+          body: JSON.stringify(newClient),
+        })
+      );
+      expect(result).toEqual(newClient);
+    });
+
+    it("handles registration failure", async () => {
+      (global.fetch as jest.Mock).mockImplementation(() => 
+        Promise.resolve({
+          ok: false,
+          status: 400,
+        })
+      );
+
+      const newClient: OAuthClientInformationFull = {
+        client_id: "new-client",
+        redirect_uris: ["https://new-client.com/callback"],
+      };
+
+      await expect(
+        provider.clientsStore.registerClient!(newClient)
+      ).rejects.toThrow(ServerError);
+    });
+  });
+
+  describe("token revocation", () => {
+    it("revokes token", async () => {
+      (global.fetch as jest.Mock).mockImplementation(() => 
+        Promise.resolve({
+          ok: true,
+        })
+      );
+
+      await provider.revokeToken!(validClient, {
+        token: "token-to-revoke",
+        token_type_hint: "access_token",
+      });
+
+      expect(global.fetch).toHaveBeenCalledWith(
+        "https://auth.example.com/revoke",
+        expect.objectContaining({
+          method: "POST",
+          headers: {
+            "Content-Type": "application/x-www-form-urlencoded",
+          },
+          body: expect.stringContaining("token=token-to-revoke"),
+        })
+      );
+    });
+
+    it("handles revocation failure", async () => {
+      (global.fetch as jest.Mock).mockImplementation(() => 
+        Promise.resolve({
+          ok: false,
+          status: 400,
+        })
+      );
+
+      await expect(
+        provider.revokeToken!(validClient, {
+          token: "invalid-token",
+        })
+      ).rejects.toThrow(ServerError);
+    });
+  });
+
+  describe("token verification", () => {
+    it("verifies valid token", async () => {
+      const authInfo = await provider.verifyAccessToken("valid-token");
+      expect(authInfo.token).toBe("valid-token");
+      expect(baseOptions.verifyToken).toHaveBeenCalledWith("valid-token");
+    });
+
+    it("rejects invalid token", async () => {
+      await expect(
+        provider.verifyAccessToken("invalid-token")
+      ).rejects.toThrow("Invalid token");
+    });
+  });
+}); 
\ No newline at end of file
diff --git a/src/server/auth/proxyProvider.ts b/src/server/auth/proxyProvider.ts
index f85ef853..d164b646 100644
--- a/src/server/auth/proxyProvider.ts
+++ b/src/server/auth/proxyProvider.ts
@@ -78,7 +78,7 @@ export class ProxyOAuthServerProvider implements OAuthServerProvider {
           headers: {
             "Content-Type": "application/x-www-form-urlencoded",
           },
-          body: params,
+          body: params.toString(),
         });
     
         if (!response.ok) {
@@ -222,7 +222,7 @@ export class ProxyOAuthServerProvider implements OAuthServerProvider {
       headers: {
         "Content-Type": "application/x-www-form-urlencoded",
       },
-      body: params,
+      body: params.toString(),
     });
 
     if (!response.ok) {