feat: add metadata endpoint

Add the metadata endpoint so that clients can get the server's
authorization and token endpoints.

Changes:

- Add a config object to allow administrators to configure the binding
  address, binding port and domain name.
- Add a target in the magefiles and a step in the CI workflow to run
  go vet.
- Add the Dockerfile.
- Replace the --address flag with the --config flag.
- Add the metadata endpoint to the router to return a JSON document
  containing the URLs to the metadata and token endpoints.

.dockerignore

@@ -0,0 +1,2 @@
+*
+!__build/indieauth-server

.forgejo/workflows/workflow.yaml

@@ -28,6 +28,10 @@ jobs:
       uses: https://codeflow.dananglin.me.uk/actions/mage-ci@main
       with:
         target: gosec
+    - name: Run go vet
+      uses: https://codeflow.dananglin.me.uk/actions/mage-ci@main
+      with:
+        target: govet
 
   style:
     name: Style

.gitignore

@@ -1,2 +1,3 @@
 /__build/*
 !__build/.gitkeep
+/.environment/*

Dockerfile

@@ -0,0 +1,5 @@
+FROM gcr.io/distroless/static-debian12
+
+COPY ./__build/indieauth-server /indieauth-server
+
+ENTRYPOINT ["/indieauth-server"]

internal/config/config.go

@@ -0,0 +1,38 @@
+package config
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+type Config struct {
+	BindAddress string `json:"bindAddress"`
+	Port        int32  `json:"port"`
+	Domain      string `json:"domain"`
+}
+
+func NewConfig(path string) (Config, error) {
+	path = filepath.Clean(path)
+
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return Config{}, fmt.Errorf(
+			"unable to read the config from %q: %w",
+			path,
+			err,
+		)
+	}
+
+	var cfg Config
+
+	if err := json.Unmarshal(data, &cfg); err != nil {
+		return Config{}, fmt.Errorf(
+			"unable to decode the JSON data: %w",
+			err,
+		)
+	}
+
+	return cfg, nil
+}

internal/executors/serve.go

@@ -3,18 +3,15 @@ package executors
 import (
 	"flag"
 	"fmt"
-	"log/slog"
-	"net/http"
-	"time"
 
-	"codeflow.dananglin.me.uk/apollo/indieauth-server/internal/info"
+	"codeflow.dananglin.me.uk/apollo/indieauth-server/internal/config"
-	"codeflow.dananglin.me.uk/apollo/indieauth-server/internal/router"
+	"codeflow.dananglin.me.uk/apollo/indieauth-server/internal/server"
 )
 
 type serveExecutor struct {
 	*flag.FlagSet
 
-	address string
+	configFile string
 }
 
 func executeServeCommand(args []string) error {
@@ -24,7 +21,7 @@ func executeServeCommand(args []string) error {
 		FlagSet: flag.NewFlagSet(executorName, flag.ExitOnError),
 	}
 
-	executor.StringVar(&executor.address, "address", "0.0.0.0:8080", "The address that the server will listen on")
+	executor.StringVar(&executor.configFile, "config", "", "The path to the config file")
 
 	if err := executor.Parse(args); err != nil {
 		return fmt.Errorf("(%s) flag parsing error: %w", executorName, err)
@@ -38,18 +35,12 @@ func executeServeCommand(args []string) error {
 }
 
 func (e *serveExecutor) execute() error {
-	server := http.Server{
+	cfg, err := config.NewConfig(e.configFile)
-		Addr:              e.address,
-		Handler:           router.NewServeMux(),
-		ReadHeaderTimeout: 1 * time.Second,
-	}
-
-	slog.Info(info.ApplicationName+" is listening for web requests", "address", e.address)
-
-	err := server.ListenAndServe()
 	if err != nil {
-		return fmt.Errorf("error running the server: %w", err)
+		return fmt.Errorf("unable to load the config: %w", err)
 	}
 
-	return nil
+	srv := server.NewServer(cfg)
+
+	return srv.Serve()
 }

internal/router/router.go

@@ -1,9 +0,0 @@
-package router
-
-import "net/http"
-
-func NewServeMux() *http.ServeMux {
-	mux := http.NewServeMux()
-
-	return mux
-}

internal/server/responses.go

@@ -0,0 +1,22 @@
+package server
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+)
+
+func sendJSONResponse(w http.ResponseWriter, statusCode int, payload any) {
+	data, err := json.Marshal(payload)
+	if err != nil {
+		slog.Error("Error marshalling the response to JSON", "error", err.Error())
+
+		w.WriteHeader(http.StatusInternalServerError)
+
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(statusCode)
+	_, _ = w.Write(data)
+}

internal/server/router.go

@@ -0,0 +1,36 @@
+package server
+
+import (
+	"fmt"
+	"net/http"
+
+	"codeflow.dananglin.me.uk/apollo/indieauth-server/internal/config"
+)
+
+func newMux(cfg config.Config) *http.ServeMux {
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("GET /.well-known/oauth-authorization-server", metadataHandleFunc(cfg.Domain))
+
+	return mux
+}
+
+func metadataHandleFunc(domain string) http.HandlerFunc {
+	return func(writer http.ResponseWriter, _ *http.Request) {
+		metadata := struct {
+			Issuer                        string   `json:"issuer"`
+			AuthorizationEndpoint         string   `json:"authorization_endpoint"`
+			TokenEndpoint                 string   `json:"token_endpoint"`
+			ServiceDocumentation          string   `json:"service_documentation"`
+			CodeChallengeMethodsSupported []string `json:"code_challenge_methods_supported"`
+		}{
+			Issuer:                        fmt.Sprintf("https://%s/", domain),
+			AuthorizationEndpoint:         fmt.Sprintf("https://%s/auth", domain),
+			TokenEndpoint:                 fmt.Sprintf("https://%s/token", domain),
+			ServiceDocumentation:          "https://indieauth.spec.indieweb.org",
+			CodeChallengeMethodsSupported: []string{"S256"},
+		}
+
+		sendJSONResponse(writer, http.StatusOK, metadata)
+	}
+}

internal/server/server.go

@@ -0,0 +1,41 @@
+package server
+
+import (
+	"fmt"
+	"log/slog"
+	"net/http"
+	"time"
+
+	"codeflow.dananglin.me.uk/apollo/indieauth-server/internal/config"
+	"codeflow.dananglin.me.uk/apollo/indieauth-server/internal/info"
+)
+
+type Server struct {
+	httpServer *http.Server
+}
+
+func NewServer(cfg config.Config) *Server {
+	address := fmt.Sprintf("%s:%d", cfg.BindAddress, cfg.Port)
+
+	httpServer := http.Server{
+		Addr:              address,
+		ReadHeaderTimeout: 1 * time.Second,
+		Handler:           newMux(cfg),
+	}
+
+	server := Server{
+		httpServer: &httpServer,
+	}
+
+	return &server
+}
+
+func (s *Server) Serve() error {
+	slog.Info(info.ApplicationName+" is now ready to serve web requests", "address", s.httpServer.Addr)
+
+	if err := s.httpServer.ListenAndServe(); err != nil {
+		return fmt.Errorf("error running the server: %w", err)
+	}
+
+	return nil
+}

magefiles/mage.go

@@ -55,10 +55,12 @@ func Lint() error {
 	return sh.RunV("golangci-lint", "run", "--color", "always")
 }
 
+// Gosec runs gosec against the code.
 func Gosec() error {
 	return sh.RunV("gosec", "./...")
 }
 
+// Staticcheck runs staticcheck against the code.
 func Staticcheck() error {
 	return sh.RunV("staticcheck", "./...")
 }
@@ -90,6 +92,11 @@ func Gofmt() error {
 	return nil
 }
 
+// Govet runs go vet against the code.
+func Govet() error {
+	return sh.RunV("go", "vet", "./...")
+}
+
 // Build build the executable.
 // To rebuild packages that are already up-to-date set PROJECT_BUILD_REBUILD_ALL=1
 // To enable verbose mode set PROJECT_BUILD_VERBOSE=1