Why are we storing the secret?

The Formatted stores the secret, so we were already storing the secret in this struct.

I added this field because the previous PR had 2 structs.

type parsedSecret struct {
	prefix string
	secret string
}

type AppSecret struct {
	// Formatted contains the secret. This value is owned by the client, not the
	// server.  It is formatted to include the prefix.
	Formatted string
	// Prefix is the ID of this secret owned by the server. When a client uses a
	// secret, this is the matching string to do a lookup on the hashed value.  We
	// cannot use the hashed value directly because the server does not store the
	// salt.
	Prefix string
	// Hashed is the server stored hash(secret,salt,...). Used for verifying a
	// secret.
	Hashed string
}

The parseFormattedSecret was in registration.go. My refactor was to make 1 struct for the AppSecret and another for HashedAppSecret. I moved ParseFormattedSecret next to GenerateSecret. I think we still need to workshop some better names to not conflate with other Secrets. Since it is in the oauth2provider package, I think that helps disambiguate it from say an APIKey secret

There is no new data being stored somewhere it was not previously.