feat!: introduce logger choice via slog (#292)

## Breaking Changes
This package now accepts a `*slog.Logger` from the Go standard library, rather than a [Lager logger](https://github.com/cloudfoundry/lager). This allows the use of alternative loggers.

- This package no longer requires you to import `code.cloudfoundry.org/lager/v3`.
- The constructors `New()`, `NewWithCustomAuth()`, `NewWithOptions()`, and also `AttachRoutes()` all take a `*slog.Logger`
- `apiresponses.FailureResponse` errors with a `ValidatedStatusCode()` method also take a `*slog.Logger` rather than a Lager logger
- The middleware `middlewares.APIVersionMiddleware` has had the `LoggerFactory` field removed, and a new field `Logger` added with type `*slog.Logger`.

If you want to continue to use Lager, you can just convert it to a `*slog.Logger`, for which you will need Lager [v3.0.3](https://github.com/cloudfoundry/lager/releases/tag/v3.0.3) for example:
```go
logger := lager.NewLogger("a-lager-logger")
router := brokerapi.New(serviceBroker, slog.New(lager.NewHandler(logger)), credentials)
```

## Reasons
Historically brokerapi has required use of the [`lager`](https://github.com/cloudfoundry/lager) logger. In Go 1.21, structured logging was introduced into the Go standard library via the [`log/slog`](https://pkg.go.dev/log/slog) package, and `slog` [compatability was added](cloudfoundry/lager@4bf4955) to `lager`.

`brokerapi` has been modified to require a `slog` logger to be passed rather than a `lager` logger. This allows users a choice of logger. Users who still want to use lager can easily do that using the lager/slog compatability.

And users who want to use `slog` or an `slog`-compatible logger can do that instead.

A key advantage is that `lager` is no longer a dependency of this package, which simplifies package management for apps that use brokerapi and other libraries which use `lager`.

Resolves #267

Author: blgm

.github/workflows/run-tests.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        version: [ 'stable', 'oldstable', '1.20' ]
+        version: [ 'stable', 'oldstable', '1.21' ]
     name: Go ${{ matrix.version }}
     outputs:
       pr_number: ${{ github.event.number }}

api.go

@@ -16,9 +16,9 @@
 package brokerapi
 
 import (
+	"log/slog"
 	"net/http"
 
-	"code.cloudfoundry.org/lager/v3"
 	"github.com/go-chi/chi/v5"
 	"github.com/pivotal-cf/brokerapi/v10/handlers"
 )
@@ -28,19 +28,19 @@ type BrokerCredentials struct {
 	Password string
 }
 
-func New(serviceBroker ServiceBroker, logger lager.Logger, brokerCredentials BrokerCredentials) http.Handler {
+func New(serviceBroker ServiceBroker, logger *slog.Logger, brokerCredentials BrokerCredentials) http.Handler {
 	return NewWithOptions(serviceBroker, logger, WithBrokerCredentials(brokerCredentials))
 }
 
-func NewWithCustomAuth(serviceBroker ServiceBroker, logger lager.Logger, authMiddleware middlewareFunc) http.Handler {
+func NewWithCustomAuth(serviceBroker ServiceBroker, logger *slog.Logger, authMiddleware middlewareFunc) http.Handler {
 	return NewWithOptions(serviceBroker, logger, WithCustomAuth(authMiddleware))
 }
 
-func AttachRoutes(router chi.Router, serviceBroker ServiceBroker, logger lager.Logger) {
+func AttachRoutes(router chi.Router, serviceBroker ServiceBroker, logger *slog.Logger) {
 	attachRoutes(router, serviceBroker, logger)
 }
 
-func attachRoutes(router chi.Router, serviceBroker ServiceBroker, logger lager.Logger) {
+func attachRoutes(router chi.Router, serviceBroker ServiceBroker, logger *slog.Logger) {
 	apiHandler := handlers.NewApiHandler(serviceBroker, logger)
 	router.Get("/v2/catalog", apiHandler.Catalog)
 

api_options.go

@@ -16,9 +16,9 @@
 package brokerapi
 
 import (
+	"log/slog"
 	"net/http"
 
-	"code.cloudfoundry.org/lager/v3"
 	"github.com/go-chi/chi/v5"
 	"github.com/pivotal-cf/brokerapi/v10/auth"
 	"github.com/pivotal-cf/brokerapi/v10/domain"
@@ -30,17 +30,13 @@ type middlewareFunc func(http.Handler) http.Handler
 type config struct {
 	router               chi.Router
 	customRouter         bool
-	logger               lager.Logger
 	additionalMiddleware []middlewareFunc
 }
 
-func NewWithOptions(serviceBroker domain.ServiceBroker, logger lager.Logger, opts ...Option) http.Handler {
-	cfg := config{
-		router: chi.NewRouter(),
-		logger: logger,
-	}
+func NewWithOptions(serviceBroker domain.ServiceBroker, logger *slog.Logger, opts ...Option) http.Handler {
+	cfg := config{router: chi.NewRouter()}
 
-	WithOptions(append(opts, withDefaultMiddleware())...)(&cfg)
+	WithOptions(append(opts, withDefaultMiddleware(logger))...)(&cfg)
 	attachRoutes(cfg.router, serviceBroker, logger)
 
 	return cfg.router
@@ -91,11 +87,11 @@ func WithEncodedPath() Option {
 	return func(*config) {}
 }
 
-func withDefaultMiddleware() Option {
+func withDefaultMiddleware(logger *slog.Logger) Option {
 	return func(c *config) {
 		if !c.customRouter {
 			defaults := []middlewareFunc{
-				middlewares.APIVersionMiddleware{LoggerFactory: c.logger}.ValidateAPIVersionHdr,
+				middlewares.APIVersionMiddleware{Logger: logger}.ValidateAPIVersionHdr,
 				middlewares.AddCorrelationIDToContext,
 				middlewares.AddOriginatingIdentityToContext,
 				middlewares.AddInfoLocationToContext,