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You don't want to be doing anything in the register method than relies on the entire app being bootstrapped; it is intended for binding classes into the container.

You should be able to use Auth in the boot() method.

If you want to do something that happens on every request you should take a look at middleware.

https://laravel.com/docs/5.4/middleware

What @tykus says is correct. The register method is there for each service provider to do their own internal setup and binding into the app.

Since you don't know the order that all the service providers will be registered you cannot rely on anything at that point.

Once all the providers are registered, the boot method is called on each

Then maybe you could suggest something? I want register service only if user is administrator? Is it possible?

You can defer the provider.

If your visitor does not need the services of the deferred SP then it won't be loaded;

https://laravel.com/docs/5.4/providers#deferred-providers