Transform the Error of a FromRequest of an Either is now impossible

[axos88]

Creating a FromRequest for a type that uses a FromRequest of an Either under the hood is now impossible to the opaque error type of the EitherExtractFut.

Migrating the following code post 4.0.0 seems impossible:

pub enum Permission {... }
pub struct Permissions(HashSet<Permission>);
pub type AuthInfo = Either<Auth0AuthData, ApiKeyAuthData>;

impl FromRequest for Auth0AuthData { ... }
impl FromRequest for ApiKeyAuthData { ... }


impl FromRequest for Permissions {
  type Error = PermissionError;
  type Future = ResponseFuture<Result<Permissions, PermissionError>>;

  fn from_request(req: &HttpRequest, _payload: &mut Payload) -> Self::Future {
    let auth_info_fut = AuthInfo::extract(req);

    let f = async move {
      let auth_info = auth_info_fut.await.map_err(|e| match e {
        EitherExtractError::Bytes(e) => PermissionError::Other(e.to_string()),
        EitherExtractError::Extract(PermissionError::NoCredentials, r) => r,
        EitherExtractError::Extract(l, _) => l,
      )?;

      match auth_info {
        Either::Left(auth0) => auth0.permissions(&config_addr).await,
        Either::Right(ApiKey { permissions, .. }) => Ok(Permissions(permissions)),
      }
    };

    Box::pin(f)
  }
}

Expected Behavior

EitherExtractError should be accessible

Current Behavior

It's opaque

Possible Solution

Revert the removal from the public api

Steps to Reproduce (for bugs)

Context

Your Environment

• Rust Version (I.e, output of rustc -V):
• Actix Web Version: 4.0.0-beta-10