Depending on [which grant](/authorization-server/which-grant/) you are implementing you will need to implement a number of repository interfaces. Each grant documentation page lists which repositories are required, and each repository interface has it's own documentation page.
The repositories are expected to return (on success) instances of [entity interfaces](https://github.com/thephpleague/oauth2-server/tree/V5-WIP/src/Entities/Interfaces); to make integration with your existing entities and models as easy as possible though, all required methods have been implemented as traits that you can use.
## Generating public and private keys
To generate the private key run this command on the terminal:
{% highlight shell %}
openssl genrsa -out private.key 1024
{% endhighlight %}
then extract the public key from the private key:
{% highlight shell %}
openssl rsa -in private.key -pubout > public.key
{% endhighlight %}
The private key must be kept secret (i.e. out of the web-root of the authorization server). The authorization server also requires the public key.
The public key should be distributed to any services (for example resource servers) that validate access tokens.
