diff --git a/.changeset/curvy-sheep-report.md b/.changeset/curvy-sheep-report.md
new file mode 100644
index 000000000..99f8ee0b0
--- /dev/null
+++ b/.changeset/curvy-sheep-report.md
@@ -0,0 +1,5 @@
+---
+'fets': patch
+---
+
+Make auth params optional if they are provided in the client options as `globalParams`
diff --git a/packages/fets/src/client/createClient.ts b/packages/fets/src/client/createClient.ts
index b80829b62..65615c5ed 100644
--- a/packages/fets/src/client/createClient.ts
+++ b/packages/fets/src/client/createClient.ts
@@ -1,7 +1,7 @@
 import { stringify as qsStringify, type IStringifyOptions } from 'qs';
 import { fetch, FormData } from '@whatwg-node/fetch';
 import { HTTPMethod } from '../typed-fetch.js';
-import { OpenAPIDocument, Router } from '../types.js';
+import { OpenAPIDocument, Router, SecurityScheme } from '../types.js';
 import { createClientTypedResponsePromise } from './clientResponse.js';
 import {
   ClientMethod,
@@ -10,6 +10,7 @@ import {
   ClientPlugin,
   ClientRequestParams,
   OASClient,
+  OASSecurityParams,
   OnFetchHook,
   OnRequestInitHook,
   OnResponseHook,
@@ -50,6 +51,33 @@ function useValidationErrors(): ClientPlugin {
 
 const EMPTY_OBJECT = {};
 
+/**
+ * Create a client for an OpenAPI document
+ * You need to pass the imported OpenAPI document as a generic
+ *
+ * We recommend using the `NormalizeOAS` type to normalize the OpenAPI document
+ *
+ * @see https://the-guild.dev/openapi/fets/client/quick-start#usage-with-existing-rest-api
+ *
+ * @example
+ * ```ts
+ * import { createClient, type NormalizeOAS } from 'fets';
+ * import type oas from './oas.ts';
+ *
+ * const client = createClient<NormalizeOAS<typeof oas>>({});
+ * ```
+ */
+export function createClient<
+  const TOAS extends OpenAPIDocument & {
+    components: { securitySchemes: Record<string, SecurityScheme> };
+  },
+>(
+  options: Omit<ClientOptionsWithStrictEndpoint<TOAS>, 'globalParams'> & {
+    globalParams: OASSecurityParams<
+      TOAS['components']['securitySchemes'][keyof TOAS['components']['securitySchemes']]
+    >;
+  },
+): OASClient<TOAS, false>;
 /**
  * Create a client for an OpenAPI document
  * You need to pass the imported OpenAPI document as a generic
@@ -77,7 +105,12 @@ export function createClient<const TOAS extends OpenAPIDocument>(
 export function createClient<const TRouter extends Router<any, any, any>>(
   options: ClientOptions,
 ): TRouter['__client'];
-export function createClient({ endpoint, fetchFn = fetch, plugins = [] }: ClientOptions) {
+export function createClient({
+  endpoint,
+  fetchFn = fetch,
+  plugins = [],
+  globalParams,
+}: ClientOptions) {
   plugins.unshift(useValidationErrors());
   const onRequestInitHooks: OnRequestInitHook[] = [];
   const onFetchHooks: OnFetchHook[] = [];
@@ -98,6 +131,44 @@ export function createClient({ endpoint, fetchFn = fetch, plugins = [] }: Client
       return new Proxy(EMPTY_OBJECT, {
         get(_target, method: HTTPMethod): ClientMethod {
           async function clientMethod(requestParams: ClientRequestParams = {}) {
+            // Merge globalParams with the current requestParams
+            if (globalParams?.headers) {
+              requestParams.headers = {
+                ...globalParams.headers,
+                ...requestParams.headers,
+              };
+            }
+            if (globalParams?.query) {
+              requestParams.query = {
+                ...globalParams.query,
+                ...requestParams.query,
+              };
+            }
+            if (globalParams?.params) {
+              requestParams.params = {
+                ...globalParams.params,
+                ...requestParams.params,
+              };
+            }
+            if (globalParams?.json) {
+              requestParams.json = {
+                ...globalParams.json,
+                ...requestParams.json,
+              };
+            }
+            if (globalParams?.formData) {
+              requestParams.formData = {
+                ...globalParams.formData,
+                ...requestParams.formData,
+              };
+            }
+            if (globalParams?.formUrlEncoded) {
+              requestParams.formUrlEncoded = {
+                ...globalParams.formUrlEncoded,
+                ...requestParams.formUrlEncoded,
+              };
+            }
+
             const {
               headers = {},
               params: paramsBody,
diff --git a/packages/fets/src/client/types.ts b/packages/fets/src/client/types.ts
index 6e881bb4e..5f783eb9b 100644
--- a/packages/fets/src/client/types.ts
+++ b/packages/fets/src/client/types.ts
@@ -183,7 +183,7 @@ export type OASParamMap<TParameters extends { name: string; in: string }[]> = Pi
   [Tuples.Map<OASParamToRequestParam<TParameters>>, Tuples.ToIntersection]
 >;
 
-export type OASClient<TOAS extends OpenAPIDocument> = {
+export type OASClient<TOAS extends OpenAPIDocument, TAuthParamsRequired extends boolean = true> = {
   /**
    * The path to be used for the request
    */
@@ -191,7 +191,12 @@ export type OASClient<TOAS extends OpenAPIDocument> = {
     /**
      * HTTP Method to be used for this request
      */
-    [TMethod in keyof OASMethodMap<TOAS, TPath>]: OASRequestParams<TOAS, TPath, TMethod> extends
+    [TMethod in keyof OASMethodMap<TOAS, TPath>]: OASRequestParams<
+      TOAS,
+      TPath,
+      TMethod,
+      TAuthParamsRequired
+    > extends
       | {
           json: {};
         }
@@ -205,10 +210,12 @@ export type OASClient<TOAS extends OpenAPIDocument> = {
           query: {};
         }
       ? (
-          requestParams: Simplify<OASRequestParams<TOAS, TPath, TMethod>> & ClientRequestInit,
+          requestParams: Simplify<OASRequestParams<TOAS, TPath, TMethod, TAuthParamsRequired>> &
+            ClientRequestInit,
         ) => ClientTypedResponsePromise<OASResponse<TOAS, TPath, TMethod>>
       : (
-          requestParams?: Simplify<OASRequestParams<TOAS, TPath, TMethod>> & ClientRequestInit,
+          requestParams?: Simplify<OASRequestParams<TOAS, TPath, TMethod, TAuthParamsRequired>> &
+            ClientRequestInit,
         ) => ClientTypedResponsePromise<OASResponse<TOAS, TPath, TMethod>>;
   };
 } & OASOAuthPath<TOAS>;
@@ -275,6 +282,7 @@ export type OASRequestParams<
   TOAS extends OpenAPIDocument,
   TPath extends keyof OASPathMap<TOAS>,
   TMethod extends keyof OASMethodMap<TOAS, TPath>,
+  TAuthParamsRequired extends boolean = true,
 > = (OASMethodMap<TOAS, TPath>[TMethod] extends {
   requestBody: { content: { 'application/json': { schema: JSONSchema } } };
 }
@@ -397,9 +405,15 @@ export type OASRequestParams<
       }
     : {}) &
   // Respect security definitions in path object
-  OASSecurityParamsBySecurityRef<TOAS, OASMethodMap<TOAS, TPath>[TMethod]> &
+  (TAuthParamsRequired extends true
+    ? OASSecurityParamsBySecurityRef<TOAS, OASMethodMap<TOAS, TPath>[TMethod]>
+    : DeepPartial<OASSecurityParamsBySecurityRef<TOAS, OASMethodMap<TOAS, TPath>[TMethod]>>) &
   // Respect global security definitions
-  OASSecurityParamsBySecurityRef<TOAS, TOAS>;
+  (TAuthParamsRequired extends true
+    ? OASSecurityParamsBySecurityRef<TOAS, TOAS>
+    : DeepPartial<OASSecurityParamsBySecurityRef<TOAS, TOAS>>);
+
+type DeepPartial<T> = T extends Record<string, any> ? { [K in keyof T]?: DeepPartial<T[K]> } : T;
 
 export type OASInput<
   TOAS extends OpenAPIDocument,
@@ -442,6 +456,10 @@ export interface ClientOptions {
    * @see https://the-guild.dev/openapi/fets/client/plugins
    */
   plugins?: ClientPlugin[];
+  /**
+   * Global parameters
+   */
+  globalParams?: ClientRequestParams;
 }
 
 export type ClientOptionsWithStrictEndpoint<TOAS extends OpenAPIDocument> = Omit<
diff --git a/packages/fets/tests/client/apiKey-test.ts b/packages/fets/tests/client/apiKey-test.ts
index a37a18d5b..b314629a4 100644
--- a/packages/fets/tests/client/apiKey-test.ts
+++ b/packages/fets/tests/client/apiKey-test.ts
@@ -1,7 +1,8 @@
 import { createClient, type NormalizeOAS } from '../../src';
 import type apiKeyExampleOas from './fixtures/example-apiKey-header-oas';
 
-const client = createClient<NormalizeOAS<typeof apiKeyExampleOas>>({});
+type NormalizedOAS = NormalizeOAS<typeof apiKeyExampleOas>;
+const client = createClient<NormalizedOAS>({});
 
 const res = await client['/me'].get({
   headers: {
@@ -15,3 +16,13 @@ if (!res.ok) {
 }
 const data = await res.json();
 console.info(`User ${data.id}: ${data.name}`);
+
+const clientWithPredefined = createClient<NormalizedOAS>({
+  globalParams: {
+    headers: {
+      'x-api-key': '123',
+    },
+  },
+});
+
+const res2 = await clientWithPredefined['/me'].get();
diff --git a/packages/fets/tests/client/global-params.spec.ts b/packages/fets/tests/client/global-params.spec.ts
new file mode 100644
index 000000000..95908ce5a
--- /dev/null
+++ b/packages/fets/tests/client/global-params.spec.ts
@@ -0,0 +1,33 @@
+import { createClient, createRouter, Response } from 'fets';
+
+describe('Client Global Params', () => {
+  it('should pass global params', async () => {
+    const router = createRouter().route({
+      path: '/test',
+      method: 'GET',
+      handler: req =>
+        Response.json({
+          headers: Object.fromEntries(req.headers.entries()),
+          query: req.query,
+        }),
+    });
+    const client = createClient<typeof router>({
+      fetchFn: router.fetch,
+      globalParams: {
+        headers: {
+          'x-api-key': '123',
+        },
+        query: {
+          foo: 'bar',
+        },
+      },
+    });
+
+    const res = await client['/test'].get();
+
+    expect(res.status).toBe(200);
+    const data = await res.json();
+    expect(data.headers['x-api-key']).toBe('123');
+    expect(data.query['foo']).toBe('bar');
+  });
+});
diff --git a/website/src/pages/client/client-configuration.mdx b/website/src/pages/client/client-configuration.mdx
index 3b804b045..96ebc5b91 100644
--- a/website/src/pages/client/client-configuration.mdx
+++ b/website/src/pages/client/client-configuration.mdx
@@ -21,3 +21,20 @@ const client = createClient<typeof oas>({
   fetch: fetchH2 as typeof fetch
 })
 ```
+
+## Global Parameters
+
+You can also pass global parameters to the `createClient` function. These parameters will be passed
+to every request made by the client.
+
+```ts
+import { oas } from './oas'
+
+const client = createClient<typeof oas>({
+  globalParams: {
+    headers: {
+      Authorization: 'Bearer 123'
+    }
+  }
+})
+```
diff --git a/website/src/pages/client/plugins.mdx b/website/src/pages/client/plugins.mdx
index 147202aef..fdf2cbd8f 100644
--- a/website/src/pages/client/plugins.mdx
+++ b/website/src/pages/client/plugins.mdx
@@ -16,41 +16,6 @@ A plugin in feTS is a function that returns an object with the following optiona
   - It enables you to modify the response or throw an error to prevent the response from being
     returned.
 
-### Custom Plugin example
-
-```ts
-import { ClientPlugin } from 'fets'
-
-export function myCustomPlugin(): ClientPlugin {
-  return {
-    onRequestInit({ requestInit }) {
-      requestInit.headers = {
-        ...requestInit.headers,
-        'X-Custom-Header': 'Custom value'
-      }
-    },
-    onFetch({ fetchFn, setFetchFn }) {
-      setFetchFn(async (input, init) => {
-        const response = await fetchFn(input, init)
-        if (response.status === 401) {
-          throw new Error('Unauthorized')
-        }
-        return response
-      })
-    },
-    onResponse({ response }) {
-      if (response.status === 401) {
-        throw new Error('Unauthorized')
-      }
-    }
-  }
-}
-
-const client = createClient<typeof someoas>({
-  plugins: [myCustomPlugin()]
-})
-```
-
 ## Handling Cookies With Built-in Cookies Plugin
 
 To handle cookies separately from the environment, you can use the `useCookieStore` plugin.