First pass at auth0 integration docs (#403)

* First pass at auth0 integration docs

* Update auth0.md

Address PR comments

* Update auth0.md

Added more detail to the section on working alongside a User model

* Update auth0.md

Wording improvement

* Update auth0.md

A few more comments

* Update auth0.md

Improved gramma

docs/guides/authentication/auth0.md

@@ -1,9 +1,170 @@
 ---
 description: Integrating with Auth0.
 sidebar_position: 6
-sidebar_label: 🚧 Auth0
+sidebar_label: Auth0
 ---
 
-# 🚧 Integrating With Auth0
+# Integrating With Auth0
+
+This guide provides simple examples of using Auth0 authentication with ZenStack. While Auth0 offers various authentication methods, this guide assumes you understand Auth0's authentication basics and can obtain a user object after authentication.
+
+## The basic premise of applying a custom session object to ZenStack.
+
+This section explains how to apply a custom session object to ZenStack by creating a user object and providing it to the enhance function when creating the Prisma client.
+
+Create a user object and provide it to the enhance function when creating the Prisma client.
+
+```ts
+export const getPrisma = async (req) => {
+  const user = await getAuthenticatedAuth0User(req);
+  return enhance(user);
+};
+```
+
+You can provide a type in the ZModel to express what the contents of the user object is.
+
+```prisma
+type Auth {
+  id             String      @id
+  specialKey     String
+  @@auth
+}
+```
+
+## Adding Auth0 authentication
+
+You can authenticate an Auth0 user and extract information from the authentication and apply it to the ZenStack session.
+
+Here's an example using a JWT:
+
+```ts
+export const getPrismaJWT = async (req) => {
+  try {
+    const jwks = jose.createRemoteJWKSet(new URL(process.env.AUTH0_JWKS_URI));
+    const token = toString(req.headers.get('authorization')).replace('Bearer ', '');
+    const res = await jose.jwtVerify(token, jwks, {
+      issuer: `${process.env.AUTH0_ISSUER_BASE_URL}/`,
+      audience: process.env.AUTH0_AUDIENCE,
+      algorithms: ['RS256'],
+    });
+
+    const userId = res.payload.sub;
+    const user = {
+      id: userId,
+      specialKey: res.payload.metadata.specialKey
+    };
+
+    return enhance(prisma, {user});
+  catch (err) {
+    // unauthenticated error
+  }  
+};
+```
+
+This would populate your `auth()` in the Zmodel with the object you've just created from auth0; enabling checks like:
+
+```prisma
+@@allow('read, update, create', auth().id == this.id)
+```
+
+or
+
+```prisma
+@@allow('read, update, create', auth().specialKey == 'SUPERMAN')
+```
+
+You can add what you need to this variable and set the types for it as referred to in the *Enhancing the prisma client* section.
+
+
+## Working along side a user model
+
+You may want to keep a record of User's in your own database.
+
+You can create your application in such a way that a lack of the user existing in the managed database triggers a process to create one, such as a user onboarding flow. 
+
+```ts
+const currentUser = async (req) => {
+  const session = await getSession(req);  // get your auth0 auth session
+
+  if (!session?.user.sub) { 
+    throw new Error('UNAUTHENTICATED');      // Throw an error if the user isn't authenticated
+  }
+
+  const dbUser = await prisma.user.findUnique({    // Find the user in the db
+    where: { id: session.user.sub },
+  }); 
+
+  return {
+    id: session.user.sub,
+    dbUserExists: !isNull(dbUser),    // If the user doesn't exist in the database, this variable can be set in the session
+  };
+};
+
+// Create the client using the currentUser
+export const getPrisma = async (req) => {
+  const user = await currentUser(req);
+  return enhance(user);
+};
+```
+
+You can use the result of this token to redirect a user to an onboarding flow, such as a signup form:
+
+```ts
+app.get('/', async (req, res) => {
+  const user = await currentUser(req);
+  if (!user.dbUserExists) {
+    res.redirect('/onboarding');
+  }
+  res.send('hello user');
+});
+```
+
+and create a user record using the ID from the Auth0 session, here's a small example using the Auth0 React SDK:
+
+```ts
+import React from "react";
+import { useAuth0 } from "@auth0/auth0-react";
+
+const Profile = () => {
+  const { user, isAuthenticated, isLoading } = useAuth0();
+  const { trigger, isMutating } = useCreateUser();
+
+  const createUser = useCallback(async (event: FormEvent<HTMLFormElement>) => {
+    const formData = new FormData(event.currentTarget);
+    const name = formData.get('name');
+
+    await trigger({
+      data: {
+        id: user.sub,
+        name: name,
+      },
+    });
+  }, [trigger, user])
+
+  return <UserForm onSubmit={createUser}/>
+};
+```
+
+
+When the client is created, the database is queried using the contents of the Auth0 token.
+
+In this case, the Auth type is what provide authentication, not the User model, for example: 
+
+```prisma
+// Specify the auth type
+type Auth {
+  id             String      @id
+  @@auth         // And decorate it with @@auth to tell ZenStack to use this as the session object
+}
+
+// add your user model as a regular model
+model User {
+  id               String          @id
+  name             String?
+  email            String?
+
+  // You can now use the Auth object, populated by Auth0, to write policies
+  @@allow('create, read, update, delete', auth().id == this.id)
+}
+```
 
-Coming soon.