fix: error hidden during discoverable login (#142)

This exposes the underlying error as a string. There needs to be some additional work in this area regardless as the idea would be to wrap the error but the current implementation doesn't explicitly implement this.

Fixes #140

webauthn/login.go

@@ -173,7 +173,7 @@ func (webauthn *WebAuthn) ValidateDiscoverableLogin(handler DiscoverableUserHand
 
  user, err := handler(parsedResponse.RawID, parsedResponse.Response.UserHandle)
  if err != nil {
- return nil, protocol.ErrBadRequest.WithDetails("Failed to lookup Client-side Discoverable Credential")
+ return nil, protocol.ErrBadRequest.WithDetails(fmt.Sprintf("Failed to lookup Client-side Discoverable Credential: %s", err))
  }
 
  return webauthn.validateLogin(user, session, parsedResponse)