Update APL documentation

docs/apl.md

@@ -14,7 +14,7 @@ APL is an interface for managing auth data of registered Apps. Implementing it d
 
 ## Example implementation
 
-Let's create an APL, which uses redis for data storage:
+Let's create an APL, which uses Redis for data storage:
 
 ```ts
 import { createClient } from "redis";
@@ -66,3 +66,74 @@ const handler = async (request) => {
 // the middleware will reject request if it's domain has not been registered
 export default withRegisteredSaleorDomainHeader({ apl: redisAPL })(handler);
 ```
+
+### Using different APL depending on the environment
+
+Depending on the environment your app is working on, you may want to use a different APL. For example during local development you might like to use `FileAPL`, because it does not require any additional infrastructure. Deployed apps on the other hand need more robust solution.
+
+To handle both scenarios, initialize the proper APLs in your code based on it's environment. In your application code:
+
+```ts
+// lib/saleorApp.ts
+
+import { FileAPL, VercelAPL } from "@saleor/app-sdk/APL";
+
+// Based on environment variable the app will use a different APL:
+// - For local development store auth data in the `.auth-data.json`.
+// - For app deployment on Vercel with Saleor CLI, use vercelAPL.
+export const apl = process.env.VERCEL === "1" ? new VercelAPL() : new FileAPL();
+```
+
+Now you can use it for in your view:
+
+```ts
+import { SALEOR_DOMAIN_HEADER } from "@saleor/app-sdk/const";
+import { withRegisteredSaleorDomainHeader } from "@saleor/app-sdk/middleware";
+import type { Handler } from "retes";
+import { toNextHandler } from "retes/adapter";
+import { Response } from "retes/response";
+
+// import created APL
+import { apl } from "@lib/saleorApp";
+
+const handler: Handler = async (request) => {
+  const saleorDomain = request.headers[SALEOR_DOMAIN_HEADER];
+
+  // Get auth data
+  const authData = apl.get(saleorDomain);
+
+  // view logic...
+
+  return Response.OK();
+};
+
+export default toNextHandler([withRegisteredSaleorDomainHeader({ apl }), handler]);
+```
+
+## Available APLs
+
+### FileAPL
+
+File based storage of auth data, intended for local development. Data are stored in the `.saleor-app-auth.json` file. You'll be able to develop app without additional dependencies or infrastructure.
+
+Please note: this APL supports single tenant only (new registrations overwrite previous ones) and should not be used on production.
+
+### VercelAPL
+
+Single tenant APL dedicated for apps deployed on Vercel. Apps deployed from Marketplace and CLI automatically set up Vercel project for this APL (`SALEOR_REGISTER_APP_URL` and `SALEOR_DEPLOYMENT_TOKEN` variables).
+
+The auth data are stored using environment variables:
+
+```mermaid
+sequenceDiagram
+    participant SI as Saleor Instance
+    participant A as App
+    participant SSI as Saleor x Vercel integration
+    participant V as Vercel
+
+    SI->>+A: Register
+    A->>SSI: Update auth data
+    A->>-SI: Register completed
+    SSI->>V: Set auth data as environment variables
+    V->>A: Redeploy the application
+```