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/error.go

@@ -3,6 +3,8 @@ package oidc
 import (
 	"errors"
 	"fmt"
+
+	"golang.org/x/exp/slog"
 )
 
 type errorType string
@@ -171,3 +173,31 @@ func DefaultToServerError(err error, description string) *Error {
 	}
 	return oauth
 }
+
+func (e *Error) LogLevel() slog.Level {
+	level := slog.LevelWarn
+	if e.ErrorType == ServerError {
+		level = slog.LevelError
+	}
+	if e.ErrorType == AuthorizationPending {
+		level = slog.LevelInfo
+	}
+	return level
+}
+
+func (e *Error) LogValue() slog.Value {
+	attrs := make([]slog.Attr, 0, 4)
+	if e.Parent != nil {
+		attrs = append(attrs, slog.Any("parent", e.Parent))
+	}
+	if e.Description != "" {
+		attrs = append(attrs, slog.String("description", e.Description))
+	}
+	if e.ErrorType != "" {
+		attrs = append(attrs, slog.String("type", string(e.ErrorType)))
+	}
+	if e.State != "" {
+		attrs = append(attrs, slog.String("state", e.State))
+	}
+	return slog.GroupValue(attrs...)
+}