feat(ssr): allow session to be used in ssr (#23)

You can now use `withSession` in `getServerSideProps` functions, like this:

```js
export const getServerSideProps = withSession(async function({ req, res }) {
  const user = req.session.get("user");

  if (user === undefined) {
    res.setHeader("location", "/login");
    res.statusCode = 302;
    res.end();
    return;
  }

  return {
    props: { user: req.session.get("user") }
  };
});
```

fixes #10

.gitignore

@@ -11,3 +11,5 @@ node_modules/
 npm-debug.log*
 yarn-debug.log*
 yarn-error.log*
+
+.now

.vscode/settings.json

@@ -2,6 +2,7 @@
   "editor.formatOnSave": true,
   "search.exclude": {
     ".yarn": true,
+    "example/.yarn": true,
     "yarn.lock": true
   },
   "eslint.packageManager": "yarn",

README.md

@@ -19,6 +19,8 @@ This method of storing session data is the same technique used by **frameworks l
 
 **By default the cookie has an ⏰ expiration time of 15 days**, set via [`maxAge`](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie#Directives). After that, even if someone tries to reuse the cookie, `next-iron-session` will not accept the underlying seal because the expiration is part of the seal value. See https://hapi.dev/family/iron for more information on @hapi/iron mechanisms.
 
+**Next.js's** 🗿[Static generation](https://nextjs.org/docs/basic-features/pages#static-generation-recommended) (SG) and ⚙️[Server-side Rendering](https://nextjs.org/docs/basic-features/pages#server-side-rendering) (SSG) are both supported.
+
 _Table of contents:_
 
 - [Installation](#installation)
@@ -44,11 +46,13 @@ npm add next-iron-session
 
 ## Usage
 
+You can find a more complete real-world example in the [example folder](./example/).
+
 The password is a private key you must pass at runtime, it has to be at least 32 characters long. Use https://1password.com/password-generator/ to generate strong passwords.
 
-Store passwords in secret environment variables on your platform.
+⚠️ Store passwords in secret environment variables on your platform.
 
-**login.js**:
+**pages/api/login.js**:
 
 ```js
 import withIronSession from "iron-session";
@@ -67,7 +71,7 @@ export default withIronSession(handler, {
 });
 ```
 
-**user.js**:
+**pages/user.js**:
 
 ```js
 import withIronSession from "iron-session";
@@ -82,7 +86,7 @@ export default withIronSession(handler, {
 });
 ```
 
-**logout.js**:
+**pages/api/logout.js**:
 
 ```js
 import withIronSession from "iron-session";

example/.gitignore

@@ -0,0 +1 @@
+.now