feat: add slog logging (#432)

* 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.

* use zitadel/logging

* finish op and testing
without middleware for now

* minimum go version 1.19

* update go mod

* log value testing only on go 1.20 or later

* finish the RP and example

* ping logging release

pkg/op/op.go

@@ -9,6 +9,7 @@ import (
 	"github.com/go-chi/chi"
 	"github.com/rs/cors"
 	"github.com/zitadel/schema"
+	"golang.org/x/exp/slog"
 	"golang.org/x/text/language"
 	"gopkg.in/square/go-jose.v2"
 
@@ -79,6 +80,9 @@ type OpenIDProvider interface {
 	DefaultLogoutRedirectURI() string
 	Probes() []ProbesFn
 
+	// EXPERIMENTAL: Will change to log/slog import after we drop support for Go 1.20
+	Logger() *slog.Logger
+
 	// Deprecated: Provider now implements http.Handler directly.
 	HttpHandler() http.Handler
 }
@@ -174,6 +178,7 @@ func newProvider(config *Config, storage Storage, issuer func(bool) (IssuerFromR
 		storage:   storage,
 		endpoints: DefaultEndpoints,
 		timer:     make(<-chan time.Time),
+		logger:    slog.Default(),
 	}
 
 	for _, optFunc := range opOpts {
@@ -217,6 +222,7 @@ type Provider struct {
 	timer                   <-chan time.Time
 	accessTokenVerifierOpts []AccessTokenVerifierOpt
 	idTokenHintVerifierOpts []IDTokenHintVerifierOpt
+	logger                  *slog.Logger
 }
 
 func (o *Provider) IssuerFromRequest(r *http.Request) string {
@@ -375,6 +381,10 @@ func (o *Provider) Probes() []ProbesFn {
 	}
 }
 
+func (o *Provider) Logger() *slog.Logger {
+	return o.logger
+}
+
 // Deprecated: Provider now implements http.Handler directly.
 func (o *Provider) HttpHandler() http.Handler {
 	return o
@@ -523,6 +533,16 @@ func WithIDTokenHintVerifierOpts(opts ...IDTokenHintVerifierOpt) Option {
 	}
 }
 
+// WithLogger lets a logger other than slog.Default().
+//
+// EXPERIMENTAL: Will change to log/slog import after we drop support for Go 1.20
+func WithLogger(logger *slog.Logger) Option {
+	return func(o *Provider) error {
+		o.logger = logger
+		return nil
+	}
+}
+
 func intercept(i IssuerFromRequest, interceptors ...HttpInterceptor) func(handler http.Handler) http.Handler {
 	issuerInterceptor := NewIssuerInterceptor(i)
 	return func(handler http.Handler) http.Handler {