# GitHub Quick Start Guide
This is a _very quick_ tutorial on how to configure your application to use
GitHub for authentication.
First you need to configure an application in your [GitHub developer
settings](https://github.com/settings/developers):
1. Click the "New OAuth App" button.
2. Set your application name to something that identifies it. You will likely
need separate applications for development and production environments, so
keep that in mind.
3. Set "Homepage URL" appropriately for your application and environment.
4. In the "Authorization callback URL" section, add your callback URL. The
callback URL is generated from the following information:
- The base URL of the application - in development that would be
`http://localhost:4000/` but in production will be your application's
URL.
- The mount point of the auth routes in your router - we'll assume
`/auth`.
- The "subject name" of the resource being authenticated - we'll assume `user`.
- The name of the strategy in your configuration. By default this is
`github`.
This means that the callback URL should look something like
`http://localhost:4000/auth/user/github/callback`.
5. Do not set "Enable Device Flow" unless you know why you want this.
6. Click "Register application".
7. Click "Generate a new client secret".
8. Copy the "Client ID" and "Client secret" somewhere safe, we'll need them
soon.
9. Click "Update application".
Next we can configure our resource (assuming you already have everything else
set up):
```elixir
defmodule MyApp.Accounts.User do
use Ash.Resource, extensions: [AshAuthentication]
authentication do
strategies do
github do
client_id MyApp.Secrets
redirect_uri MyApp.Secrets
client_secret MyApp.Secrets
end
end
end
end
```
Because all the configuration values should be kept secret (ie the
`client_secret`) or are likely to be different for each environment we use the
`AshAuthentication.Secret` behaviour to provide them. In this case we're
delegating to the OTP application environment, however you may want to use a
system environment variable or some other secret store (eg Vault).
```elixir
defmodule MyApp.Secrets do
use AshAuthentication.Secret
def secret_for([:authentication, :strategies, :github, :client_id], MyApp.Accounts.User, _) do
get_config(:client_id)
end
def secret_for([:authentication, :strategies, :github, :redirect_uri], MyApp.Accounts.User, _) do
get_config(:redirect_uri)
end
def secret_for([:authentication, :strategies, :github, :client_secret], MyApp.Accounts.User, _) do
get_config(:client_secret)
end
defp get_config(key) do
:my_app
|> Application.get_env(:github, [])
|> Keyword.fetch(key)
end
end
```
The values for this configuration should be:
* `client_id` - the client ID copied from the GitHub settings page.
* `redirect_uri` - the URL to the generated auth routes in your application
(eg `http://localhost:4000/auth`).
* `client_secret` the client secret copied from the GitHub settings page.
Lastly, we need to add a register action to your user resource. This is defined
as an upsert so that it can register new users, or update information for
returning users. The default name of the action is `register_with_` followed by
the strategy name. In our case that is `register_with_github`.
The register action takes two arguments, `user_info` and the `oauth_tokens`.
- `user_info` contains the [`GET /user` response from
GitHub](https://docs.github.com/en/rest/users/users?apiVersion=2022-11-28#get-the-authenticated-user)
which you can use to populate your user attributes as needed.
- `oauth_tokens` contains the [`POST /login/oauth/access_token` response from
GitHub](https://docs.github.com/en/developers/apps/building-oauth-apps/authorizing-oauth-apps#response)
- you may want to store these if you intend to call the GitHub API on behalf
of the user.
```elixir
defmodule MyApp.Accounts.User do
use Ash.Resource, extensions: [AshAuthentication]
# ...
actions do
create :register_with_github do
argument :user_info, :map, allow_nil?: false
argument :oauth_tokens, :map, allow_nil?: false
upsert? true
upsert_identity :email
# Required if you have token generation enabled.
change AshAuthentication.GenerateTokenChange
# Required if you have the `identity_resource` configuration enabled.
change AshAuthentication.Strategy.OAuth2.IdentityChange
change fn changeset, _ ->
user_info = Ash.Changeset.get_argument(changeset, :user_info)
Ash.Changeset.change_attributes(changeset, Map.take(user_info, ["email"]))
end
end
end
# ...
end
```
