Add publisher docs from h repo into this repo

These are documentation files intended for publishers who're embedding h
in their sites, they're being removed from the h repo into this client
repo.

There may be some reStructuredText syntax in these files that doesn't
work on GitHub (only in Sphinx or only on readthedocs) but these client
docs are about to be moved over to Sphinx/readthedocs anyway.

docs/publishers/authorization-grant-tokens.rst

+Generating authorization grant tokens
+#####################################
+
+.. warning::
+
+   This document describes an integration mechanism that is undergoing
+   early-stage testing. The details of the token format may change in the
+   future.
+
+In order to allow your users (i.e. those whose accounts and authentication
+status you control) to annotate using a copy of Hypothesis embedded on your
+pages, you can ask us to register your site as a special kind of OAuth client.
+
+We will issue you with a :term:`Client ID` and a :term:`Client secret`. These
+will allow you generate time-limited "authorization grant tokens" which can be
+supplied as configuration to the Hypothesis sidebar, and which will allow your
+users to annotate without needing to log in again. This document describes how
+to generate those tokens.
+
+Overview
+--------
+
+You will have been provided with the following:
+
+.. glossary::
+
+   Client ID
+      A unique identifier for your client account. It's a UUID and will look
+      something like this: ``4a2fa3b4-c160-4436-82d3-148f602c9aa8``
+
+   Client secret
+      A secret string which you MUST NOT reveal publicly, and which is used to
+      cryptographically sign the grant tokens you will generate.
+
+In addition, you will have provided us with what we call an "authority" for your
+account. The authority is a DNS domain name and acts as a unique namespace for
+your user's accounts. For example, if your site lives at
+``https://example.com``, you may choose to use ``example.com`` as your
+authority, although we do not currently require any particular correspondence
+between your web address and your account authority.
+
+You will use these three pieces of information, in combination with your user's
+unique usernames, to generate the grant token.
+
+The grant token is a `JSON Web Token (JWT) <https://jwt.io/>`_ and we strongly
+recommend that you use an existing JWT library for your programming environment
+if you can. You can find `a list of JWT client libraries here
+<https://jwt.io/#libraries-io>`_.
+
+Token format
+------------
+
+A grant token is a JWT, signed with the :term:`Client secret` using the
+``HS256`` algorithm, with a payload in a specific format, given below. Let's
+assume that:
+
+- Your :term:`Client ID` is ``4a2fa3b4-c160-4436-82d3-148f602c9aa8``.
+- Your authority is ``customwidgets.com``.
+- The user has a username of ``samina.mian``.
+- The current time is ``2016-11-08T11:35:45Z``, which corresponds to a UTC Unix
+  timestamp of ``1478601345``.
+- The token should be valid for a few minutes, e.g. until ``1478601645``,
+  expressed as a UTC Unix timestamp. The server limits the lifetime of a token
+  (the difference between the ``nbf`` and ``exp`` timestamps) to 10 minutes.
+- The token should be valid for the annotation service running at
+  ``hypothes.is``.
+
+With these data, we can construct a token payload. It should look like the
+following::
+
+   {
+     "aud": "hypothes.is",
+     "iss": "4a2fa3b4-c160-4436-82d3-148f602c9aa8",
+     "sub": "acct:samina.mian@customwidgets.com",
+     "nbf": 1478601345,
+     "exp": 1478601645
+   }
+
+You should sign this payload using the ``HS256`` JWT-signing algorithm, using
+the :term:`Client secret` as the key. The result will look something like this::
+
+   eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiI0QTJGQTNCNC1DMTYwLTQ0MzYtODJEMy0xNDhGNjAyQzlBQTgiLCJuYmYiOjE0Nzg2MDEzNDUsImF1ZCI6Imh5cG90aGVzLmlzIiwiZXhwIjoxNDc4NjAxOTQ1LCJzdWIiOiJhY2N0OnNhbWluYS5taWFuQGN1c3RvbXdpZGdldHMuY29tIn0.65-ZErbLu1q8LpT_K8FAOQO984hAyN1XFBe1rC3lgfk
+
+.. seealso::
+
+   `RFC7523 <https://tools.ietf.org/html/rfc7523>`_, "JSON Web Token (JWT)
+   Profile for OAuth 2.0 Client Authentication and Authorization Grants". Note
+   that we currently only support the ``HS256`` signing algorithm, and not the
+   public-key ``RS256`` signing algorithm mentioned in the RFC.
+
+Examples
+--------
+
+This section contains complete example code for generating a JWT in various
+common programming environments.
+
+Python
+``````
+
+We recommend using `PyJWT <https://pyjwt.readthedocs.io/en/latest/>`_::
+
+   import datetime
+   import jwt
+
+   # IMPORTANT: replace these values with those for your client account!
+   CLIENT_AUTHORITY = 'customwidgets.com'
+   CLIENT_ID        = '4a2fa3b4-c160-4436-82d3-148f602c9aa8'
+   CLIENT_SECRET    = '5SquUVG0Tpg57ywoxUbPPgjtK0OkX1ttipVlfBRRrpo'
+
+   def generate_grant_token(username):
+      now = datetime.datetime.utcnow()
+      userid = 'acct:{username}@{authority}'.format(username=username,
+                                                    authority=CLIENT_AUTHORITY)
+      payload = {
+         'aud': 'hypothes.is',
+         'iss': CLIENT_ID,
+         'sub': userid,
+         'nbf': now,
+         'exp': now + datetime.timedelta(minutes=10),
+      }
+      return jwt.encode(payload, CLIENT_SECRET, algorithm='HS256')
+
+Ruby
+````
+
+We recommend using `ruby-jwt <https://jwt.github.io/ruby-jwt/>`_::
+
+   require 'jwt'
+
+   # IMPORTANT: replace these values with those for your client account!
+   CLIENT_AUTHORITY = 'customwidgets.com'
+   CLIENT_ID        = '4a2fa3b4-c160-4436-82d3-148f602c9aa8'
+   CLIENT_SECRET    = '5SquUVG0Tpg57ywoxUbPPgjtK0OkX1ttipVlfBRRrpo'
+
+   def generate_grant_token(username)
+     now = Time.now.to_i
+     userid = "acct:#{username}@#{CLIENT_AUTHORITY}"
+     payload = {
+       aud: "hypothes.is",
+       iss: CLIENT_ID,
+       sub: userid,
+       nbf: now,
+       exp: now + 600
+     }
+     JWT.encode payload, CLIENT_SECRET, 'HS256'
+   end

docs/publishers/embedding.rst

+How to add Hypothesis to your website
+#####################################
+
+.. If you update this page, please ensure you update the "For Publishers" page
+   on the Hypothesis website, or coordinate with someone who can
+   (https://hypothes.is/for-publishers/).
+
+To add Hypothesis to your website, add the following line to the HTML source of
+your page:
+
+.. code-block:: html
+
+   <script src="https://hypothes.is/embed.js" async></script>
+
+You can configure Hypothesis by including a config tag above the the script tag.
+For example, the following arrangement will ensure that our yellow highlights
+are hidden by default:
+
+.. code-block:: html
+
+   <script type="application/json" class="js-hypothesis-config">
+   {"showHighlights": false}
+   </script>
+   <script src="https://hypothes.is/embed.js" async></script>
+
+You can find the `full list of configuration options
+<https://github.com/hypothesis/client/blob/master/docs/config.md>`_ in our
+client documentation.

docs/publishers/index.rst

+Advice for publishers
+#####################
+
+If you publish content on the web and want to allow people to annotate your
+content, the following documents will help you get started.
+
+.. toctree::
+   :maxdepth: 1
+
+   embedding
+   authorization-grant-tokens