diff --git a/src/Sage.ts b/src/Sage.ts
index 45ed25a..a2e79ea 100644
--- a/src/Sage.ts
+++ b/src/Sage.ts
@@ -13,7 +13,8 @@ import {
   statusCodeToMessage,
   parseJsonStr,
   isRedirect,
-  isError
+  isError,
+  wrapArray
 } from './utils.js';
 import { SageHttpResponse } from './SageHttpResponse.js';
 import path from 'node:path';
@@ -69,6 +70,10 @@ export class Sage {
     this.client = new Client(`http://localhost:${port}`, httpClientOptions);
   }
 
+  /**
+   * Sets query parameters for the request.
+   * @param query
+   */
   query(query: Record<string | number, string>): this {
     this.request.query = query;
     return this;
@@ -104,28 +109,54 @@ export class Sage {
    * @param key
    * @param value
    */
-  set(key: string, value: string): this {
-    this.request.headers = { ...(this.request.headers || {}), [key]: value };
+  set(key: string, value: string | string[]): this {
+    if (!this.request.headers) {
+      this.request.headers = {};
+    }
+
+    value = wrapArray(value);
+
+    // If already an array
+    if (Array.isArray(this.request.headers[key])) {
+      const existingValue = this.request.headers[key] as string[];
+      existingValue.push(...value);
+      return this;
+    }
+
+    // If an existing value is a string, convert it to an array
+    if (typeof this.request.headers[key] === 'string') {
+      const existingValue = this.request.headers[key] as string;
+      this.request.headers[key] = [existingValue, ...value];
+      return this;
+    }
+
+    // If a single value is passed, don't wrap it in an array
+    if (value.length === 1) {
+      this.request.headers[key] = value[0];
+      return this;
+    }
+
+    this.request.headers[key] = value;
     return this;
   }
 
   /**
-   * Sets the Authorization header to base64 of Bearer token with a Basic Prefix.
-   * @param username
+   * If password is provided, it will be used to create a Basic Auth header.
+   * If password is not provided, it will be used as a Bearer token.
+   * Automatically adds Basic or Bearer prefix to the token.
+   * @param usernameOrToken
    * @param password
    */
-  basic(username: string, password: string): this {
-    const encoded = Buffer.from(`${username}:${password}`).toString('base64');
-    this.set('Authorization', `Basic ${encoded}`);
-    return this;
-  }
+  auth(usernameOrToken: string, password?: string): this {
+    if (password) {
+      const credentials = Buffer.from(
+        `${usernameOrToken}:${password}`
+      ).toString('base64');
+      this.set('Authorization', `Basic ${credentials}`);
+      return this;
+    }
 
-  /**
-   * Sets the Authorization header to Bearer token. The prefix will be added.
-   * @param token
-   */
-  bearer(token: string): this {
-    this.set('Authorization', `Bearer ${token}`);
+    this.set('Authorization', `Bearer ${usernameOrToken}`);
     return this;
   }
 
@@ -254,7 +285,24 @@ export class Sage {
       } satisfies SageHttpResponse);
     } catch (e) {
       throw new SageException(
-        `Failed to make a request to the underlying server, please take a look at the upstream error for more details: `,
+        `
+    Failed;
+    to;
+    make;
+    a;
+    request;
+    to;
+    the;
+    underlying;
+    server, please;
+    take;
+    a;
+    look;
+    at;
+    the;
+    upstream;
+    error;
+    for more details: `,
         e
       );
     } finally {
diff --git a/src/utils.ts b/src/utils.ts
index c53039d..cc3db60 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -78,3 +78,11 @@ export const isObject = (candidate: unknown): candidate is object => {
 export const copyObject = <T>(obj: T): T => {
   return JSON.parse(JSON.stringify(obj));
 };
+
+export const wrapArray = <T>(value: T | T[]): T[] => {
+  if (Array.isArray(value)) {
+    return value;
+  }
+
+  return [value];
+};
diff --git a/test/Sage.spec.ts b/test/Sage.spec.ts
index fd5188b..fca0105 100644
--- a/test/Sage.spec.ts
+++ b/test/Sage.spec.ts
@@ -1,12 +1,16 @@
 import { createServer } from 'node:http';
 import { Sage } from '../src/Sage.js';
 import { getExpressApp, getFastifyApp } from './utils.js';
+import { ConfigStore } from '../src/ConfigStore.js';
+import { SAGE_DEFAULT_CONFIG } from '../src/index.js';
 
 describe('Sage', () => {
   it('should initialize sage assistant', async () => {
     const expressServer = createServer(getExpressApp());
     const fastifyServer = getFastifyApp();
     const server = createServer();
+    const store = new ConfigStore(SAGE_DEFAULT_CONFIG);
+    const config = store.getConfig();
 
     const sage1 = new Sage(
       {
@@ -18,7 +22,8 @@ describe('Sage', () => {
         launched: false
       },
       'GET',
-      '/test'
+      '/test',
+      config
     );
     const sage2 = new Sage(
       {
@@ -30,7 +35,8 @@ describe('Sage', () => {
         launched: false
       },
       'GET',
-      '/test'
+      '/test',
+      config
     );
     const sage3 = new Sage(
       {
@@ -40,9 +46,9 @@ describe('Sage', () => {
         launched: false
       },
       'GET',
-      '/test'
+      '/test',
+      config
     );
-
     expect(sage1).toBeTruthy();
     expect(sage2).toBeTruthy();
     expect(sage3).toBeTruthy();
diff --git a/test/index.spec.ts b/test/index.spec.ts
index 64cabad..3947fd0 100644
--- a/test/index.spec.ts
+++ b/test/index.spec.ts
@@ -372,6 +372,70 @@ describe('request', () => {
         });
       });
     });
+    describe('header', () => {
+      it('should set and pass a single header', async () => {
+        const res = await request(expressApp)
+          .post('/ping-pong')
+          .set('x-custom-header', 'custom-value');
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value'
+            }
+          }
+        } as SageHttpResponse);
+      });
+
+      it('should set and pass 2 values in a single header', async () => {
+        const res = await request(expressApp)
+          .post('/ping-pong')
+          .set('x-custom-header', 'custom-value1')
+          .set('x-custom-header', 'custom-value2');
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value1, custom-value2'
+            }
+          }
+        } as SageHttpResponse);
+      });
+
+      it('should set and pass 3 values in a single header', async () => {
+        const res = await request(expressApp)
+          .post('/ping-pong')
+          .set('x-custom-header', 'custom-value1')
+          .set('x-custom-header', 'custom-value2')
+          .set('x-custom-header', 'custom-value3');
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value1, custom-value2, custom-value3'
+            }
+          }
+        } as SageHttpResponse);
+      });
+
+      it('should accept arrays', async () => {
+        const res = await request(expressApp)
+          .post('/ping-pong')
+          .set('x-custom-header', [
+            'custom-value1',
+            'custom-value2',
+            'custom-value3'
+          ]);
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value1, custom-value2, custom-value3'
+            }
+          }
+        } as SageHttpResponse);
+      });
+    });
   });
 
   describe('fastify', () => {
@@ -604,5 +668,84 @@ describe('request', () => {
         } as SageHttpResponse);
       });
     });
+
+    describe('header', () => {
+      it('should set and pass a single header', async () => {
+        const res = await request(fastifyApp.server)
+          .post('/ping-pong')
+          .set('x-custom-header', 'custom-value');
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value'
+            }
+          }
+        } as SageHttpResponse);
+      });
+
+      it('should set and pass 2 values in a single header', async () => {
+        const res = await request(fastifyApp.server)
+          .post('/ping-pong')
+          .set('x-custom-header', 'custom-value1')
+          .set('x-custom-header', 'custom-value2');
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value1, custom-value2'
+            }
+          }
+        } as SageHttpResponse);
+      });
+
+      it('should set and pass 3 values in a single header', async () => {
+        const res = await request(fastifyApp.server)
+          .post('/ping-pong')
+          .set('x-custom-header', 'custom-value1')
+          .set('x-custom-header', 'custom-value2')
+          .set('x-custom-header', 'custom-value3');
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value1, custom-value2, custom-value3'
+            }
+          }
+        } as SageHttpResponse);
+      });
+
+      it('should accept array with multiple values', async () => {
+        const res = await request(fastifyApp.server)
+          .post('/ping-pong')
+          .set('x-custom-header', [
+            'custom-value1',
+            'custom-value2',
+            'custom-value3'
+          ]);
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value1, custom-value2, custom-value3'
+            }
+          }
+        } as SageHttpResponse);
+      });
+
+      it('should accept arrays with a single value', async () => {
+        const res = await request(fastifyApp.server)
+          .post('/ping-pong')
+          .set('x-custom-header', ['custom-value1']);
+
+        expect(res).toMatchObject({
+          body: {
+            reqHeaders: {
+              'x-custom-header': 'custom-value1'
+            }
+          }
+        } as SageHttpResponse);
+      });
+    });
   });
 });