Create module that will use https://http4s.org/ for http client.

Currently, accessible zio-macro does not support generic E and O types in Service: zio/zio-macros#60

Once this is fixed, KeyReaders should be abstracted, being polymorphic in output type:

@accessible(">")
trait KeyReader[A] {
  val serviceAccountKeyReader: KeyReader.Service[Any, A]
}



object KeyReader {
  trait Service[R, A] {
    def readKey(path: String): ZIO[R, KeyError, A]
  }
}

Currently core of the lib depends on http4s and has default live implementation that requires that users provide org.http4s.Client[F] instance. That will import unnecessary libraries for users that don't want to use http4s live implementation. It would be better to seprate library in 3 subprojects:

• core (default implementation of auth services with no dependency on http clients) #11
• http4s (implementation of http client using http4s lib) #10
• sttp (implementation of http client using sttp lib) #9

Create core module in which Authenticator with default implementation that will depend on abstract services.

Create module that will use https://github.com/softwaremill/sttp for http client.

Implement OAuth 2.0 for Web Server Applications API.
Flow is described here https://developers.google.com/identity/protocols/OAuth2WebServer.
There is good example how to model API in Functional Programming for Mortals book, section 4.3 Modelling OAuth2