docs: update docs (#8)

Author: romanindev

docs/v1/api-reference.md

@@ -1,24 +1,222 @@
 # Auth
 
-`@dfsync/client` supports auth configuration so you can attach tokens or other credentials to requests.
+`@dfsync/client` supports three auth strategies:
 
-This allows you to centralize auth logic instead of repeating it in every request.
+- bearer token
+- API key
+- custom auth
 
-## Example
+Auth is configured once at client creation time.
+
+## Bearer token
 
 ```ts
-import { createClient } from '@dfsync/client';
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'bearer',
+    token: 'secret-token',
+  },
+});
+```
+
+This adds:
 
+```http
+authorization: Bearer secret-token
+```
+
+## Async bearer token
+
+You can resolve the token lazily:
+
+```ts
 const client = createClient({
-  baseURL: 'https://api.example.com',
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'bearer',
+    token: async () => {
+      return process.env.API_TOKEN!;
+    },
+  },
+});
+```
+
+## Custom bearer header name
 
-  auth: async ({ request }) => {
-    request.headers.set('Authorization', 'Bearer TOKEN');
+```ts
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'bearer',
+    token: 'secret-token',
+    headerName: 'x-authorization',
   },
 });
 ```
 
-Every request sent by the client will include the Authorization header.
+## API key in header
+
+By default, API key auth uses header mode and the header name `x-api-key`.
+
+```ts
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'apiKey',
+    value: 'api-key-123',
+  },
+});
+```
+
+This adds:
+
+```http
+x-api-key: api-key-123
+```
+
+## Async API key resolver
+
+```ts
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'apiKey',
+    value: async () => {
+      return process.env.API_KEY!;
+    },
+  },
+});
+```
+
+## Custom API key header name
+
+```ts
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'apiKey',
+    value: 'api-key-123',
+    name: 'x-service-key',
+  },
+});
+```
+
+## API key in query string
+
+```ts
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'apiKey',
+    value: 'query-key',
+    in: 'query',
+    name: 'api_key',
+  },
+});
+```
+
+A request like:
+
+```ts
+await client.get('/users', {
+  query: { page: 1 },
+});
+```
+
+becomes:
+
+```text
+https://api.example.com/users?page=1&api_key=query-key
+```
+
+## Custom auth
+
+Use custom auth when you need full control over headers and URL mutation.
+
+```ts
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  auth: {
+    type: 'custom',
+    apply: ({ headers, url, request }) => {
+      headers['x-service-name'] = 'billing-worker';
+      url.searchParams.set('tenant', 'acme');
+    },
+  },
+});
+```
+
+## Auth context
+
+Custom auth receives:
+
+```ts
+{
+  (request, url, headers);
+}
+```
+
+This lets you inspect the request and modify the final URL or headers before the request is sent.
+
+## Auth execution order
+
+Auth runs before `beforeRequest` hooks.
+
+That means `beforeRequest` hooks can see and further modify headers or query params already produced by auth.
+
+## Auth precedence
+
+If auth writes to a header that already exists, auth wins.
+
+Example:
+
+```ts
+const client = createClient({
+  baseUrl: 'https://api.example.com',
+  headers: {
+    authorization: 'Bearer old-token',
+  },
+  auth: {
+    type: 'bearer',
+    token: 'new-token',
+  },
+});
+```
+
+Final header:
+
+```http
+authorization: Bearer new-token
+```
+
+## Auth config reference
+
+```ts
+type AuthValueResolver = string | (() => string | Promise<string>);
+
+type BearerAuthConfig = {
+  type: 'bearer';
+  token: AuthValueResolver;
+  headerName?: string;
+};
+
+type ApiKeyAuthConfig = {
+  type: 'apiKey';
+  value: AuthValueResolver;
+  in?: 'header' | 'query';
+  name?: string;
+};
+
+type CustomAuthConfig = {
+  type: 'custom';
+  apply: (ctx: {
+    request: RequestConfig;
+    url: URL;
+    headers: Record<string, string>;
+  }) => void | Promise<void>;
+};
+```
 
 ## Common use cases