feat(op): user slog for logging

integrate with golang.org/x/exp/slog for logging.
provide a middleware for request scoped logging.

BREAKING CHANGES:

1. OpenIDProvider and sub-interfaces get a Logger()
method to return the configured logger;
2. AuthRequestError now takes the complete Authorizer,
instead of only the encoder. So that it may use its Logger() method.
3. RequestError now takes a Logger as argument.

pkg/oidc/authorization.go

@@ -1,5 +1,11 @@
 package oidc
 
+import (
+	"fmt"
+
+	"golang.org/x/exp/slog"
+)
+
 const (
 	// ScopeOpenID defines the scope `openid`
 	// OpenID Connect requests MUST contain the `openid` scope value
@@ -86,6 +92,15 @@ type AuthRequest struct {
 	RequestParam string `schema:"request"`
 }
 
+func (a *AuthRequest) LogValue() slog.Value {
+	return slog.GroupValue(
+		slog.Any("scopes", fmt.Stringer(a.Scopes)),
+		slog.String("response_type", string(a.ResponseType)),
+		slog.String("client_id", a.ClientID),
+		slog.String("redirect_uri", a.RedirectURI),
+	)
+}
+
 // GetRedirectURI returns the redirect_uri value for the ErrAuthRequest interface
 func (a *AuthRequest) GetRedirectURI() string {
 	return a.RedirectURI