docs: add doc(en) for express adapter package (#577)

docs/en/Host-Skill-As-Webservice.rst

@@ -0,0 +1,125 @@
+====================================
+Host a Custom Skill as a Web Service
+====================================
+
+You can build a custom skill for Alexa by implementing a web service that
+accepts requests from and sends responses to the Alexa service in the cloud.
+
+The web service must meet certain requirements to handle requests sent by Alexa
+and adhere to the Alexa Skills Kit interface standards. For more information,
+see
+`Alexa Skills Kit technical documentation <https://developer.amazon.com/docs/custom-skills/host-a-custom-skill-as-a-web-service.html>`__.
+
+ASK SDK Express Adapter
+---------------------------
+
+The Alexa Skills Kit SDK (ASK SDK) for Node provides boilerplate code for 
+request and timestamp verification through the
+`ask-sdk-express-adapter <https://www.npmjs.com/package/ask-sdk-express-adapter/>`__
+package. This package provides the verification components by exporting
+the `SkillRequestSignatureVerifier class <https://github.com/alexa/alexa-skills-kit-sdk-for-nodejs/blob/2.0.x/ask-sdk-express-adapter/lib/verifier/index.ts#L56/>`__
+and `TimestampVerifier class <https://github.com/alexa/alexa-skills-kit-sdk-for-nodejs/blob/2.0.x/ask-sdk-express-adapter/lib/verifier/index.ts#L292/>`__.
+Also this package provides `ExpressAdapter class <https://github.com/alexa/alexa-skills-kit-sdk-for-nodejs/blob/2.0.x/ask-sdk-express-adapter/lib/adapter/ExpressAdapter.ts#L24/>`__ 
+which assembles the verification ability and skill invocation ability,
+making it easier to register requestHandlers on your `express application <http://expressjs.com/en/5x/api.html#app/>`__.
+
+Installation
+~~~~~~~~~~~~
+
+You can add the ``ask-sdk-express-adapter`` package to your skill project through NPM:
+``npm install --save ask-sdk-express-adapter``.
+
+
+For web application with express framework
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The `ExpressAdapter <https://github.com/alexa/alexa-skills-kit-sdk-for-nodejs/blob/2.0.x/ask-sdk-express-adapter/lib/adapter/ExpressAdapter.ts#L24/>`__
+class registers the skill instance from
+the ``SkillBuilder`` object, and provides a ``getRequestHandlers``
+method that return an array of request handlers which can be registed
+to your Express application.
+
+You can enable or disable request or timestamp
+verification for testing purposes by setting the boolean parameters
+``verifySignature`` and ``verifyTimeStamp`` on the
+``ExpressAdapter`` instance. You can also provide additional custom
+verifiers that need to be applied on the input request before skill invocation.
+
+Usage
+~~~~~
+
+.. tabs::
+
+  .. code-tab:: javascript
+    const Alexa = require('ask-sdk-core');
+    const express = require('express');
+    const { ExpressAdapter } = require('ask-sdk-express-adapter');
+
+    const app = express();
+    const skillBuilder = Alexa.SkillBuilders.custom();
+    const skill = skillBuilder.create();
+    const adapter = new ExpressAdapter(skill, true, true);
+
+    app.post('/', adapter.getRequestHandlers());
+    app.listen(3000);
+
+  .. code-tab:: typescript
+    import * as Alexa from 'ask-sdk-core';
+    import express from 'express';
+    import { ExpressAdapter } from 'ask-sdk-express-adapter';
+
+    const app = express();
+    const skillBuilder = Alexa.SkillBuilders.custom();
+    const skill = skillBuilder.create();
+    const adapter = new ExpressAdapter(skill, true, true);
+
+    app.post('/', adapter.getRequestHandlers());
+    app.listen(3000);
+
+
+For web application without Express framework
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you don't use Express framework, 
+the `SkillRequestSignatureVerifier <https://github.com/alexa/alexa-skills-kit-sdk-for-nodejs/blob/2.0.x/ask-sdk-express-adapter/lib/verifier/index.ts#L56/>`__
+and `TimestampVerifier <https://github.com/alexa/alexa-skills-kit-sdk-for-nodejs/blob/2.0.x/ask-sdk-express-adapter/lib/verifier/index.ts#L292/>`__
+are provided for you to use in your web application.
+
+Usage
+~~~~~
+
+.. tabs::
+
+  .. code-tab:: javascript
+    const Alexa = require('ask-sdk-core');
+    const { SkillRequestSignatureVerifier, TimestampVerifier } = require('ask-sdk-express-adapter');
+
+    const skillBuilder = Alexa.SkillBuilders.custom();
+    const skill = skillBuilder.create();
+
+    // This code snippet assumes you have already consumed the request body as text and headers
+    try {
+        await new SkillRequestSignatureVerifier().verify(textBody, requestHeaders);
+        await new TimestampVerifier().verify(textBody);
+    } catch (err) {
+        // server return err message
+    }
+    const response = skill.invoke(JSON.parse(textBody));
+    // server send response in Json format
+
+  .. code-tab:: typescript
+    import * as Alexa from 'ask-sdk-core';
+    import { SkillRequestSignatureVerifier, TimestampVerifier } from 'ask-sdk-express-adapter';
+
+    const skillBuilder = Alexa.SkillBuilders.custom();
+    const skill = skillBuilder.create();
+
+    // This code snippet assumes you have already consumed the request body as text and headers
+    try {
+        await new SkillRequestSignatureVerifier().verify(textBody, requestHeaders);
+        await new TimestampVerifier().verify(textBody);
+    } catch (err) {
+        // server return err message
+    }
+    const response = skill.invoke(JSON.parse(textBody));
+    // server send response in Json format