feat: add env-driven configuration

AGENTS.md

@@ -24,7 +24,7 @@ Trust `gofmt`; avoid manual formatting. Use CamelCase for exported Go identifier
 
 ## Testing Guidelines
 
-Adopt Go’s `testing` package with table-driven cases. Name files `<feature>_test.go`, colocated with the code under test. Run `go test ./...` (and `go test -cover ./...` for major features) before opening a PR, ensuring new branches maintain or raise coverage.
+Adopt Go’s `testing` package with table-driven cases. Name files `<feature>_test.go`, colocated with the code under test. Run `go test ./... -cover -count=1` before opening a PR so coverage is measured on fresh binaries; we don’t enforce a target, but avoid notable drops when adding code.
 
 ## Commit & Pull Request Guidelines
 

cmd/server/main.go

@@ -6,29 +6,37 @@ import (
 	"net/http"
 	"os"
 
+	"github.com/rjnemo/auth/internal/config"
 	"github.com/rjnemo/auth/internal/logging"
 	"github.com/rjnemo/auth/internal/server"
-	"gorm.io/gorm/logger"
 )
 
-const listenAddr = ":8000"
-
 func main() {
-	if err := run(logger); err != nil {
+	baseLogger := logging.New(os.Stdout, logging.ModeText, &slog.HandlerOptions{AddSource: true})
+
+	cfg, err := config.New()
+	if err != nil {
+		baseLogger.Error("configuration error", slog.Any("error", err))
+		os.Exit(1)
+	}
+
+	logger := logging.New(os.Stdout, cfg.LogMode, &slog.HandlerOptions{AddSource: cfg.Environment == "development"})
+	logger = logger.With(slog.String("env", cfg.Environment))
+
+	if err := run(cfg, logger); err != nil {
 		logger.Error("server exited", slog.Any("error", err))
 		os.Exit(1)
 	}
 }
 
-func run() error {
-	logger := logging.New(os.Stdout, logging.ModeText, &slog.HandlerOptions{AddSource: true})
-	srv, err := server.New(logger)
+func run(cfg *config.Config, logger *slog.Logger) error {
+	srv, err := server.New(*cfg, logger)
 	if err != nil {
 		return fmt.Errorf("initialise server: %w", err)
 	}
 
-	logger.Info("starting server", slog.String("addr", listenAddr))
-	if err := http.ListenAndServe(listenAddr, srv.Router()); err != nil {
+	logger.Info("starting server", slog.String("addr", fmt.Sprintf("http://localhost%s", cfg.ListenAddr)))
+	if err := http.ListenAndServe(cfg.ListenAddr, srv.Router()); err != nil {
 		return fmt.Errorf("listen: %w", err)
 	}
 

internal/config/config.go

@@ -0,0 +1,58 @@
+package config
+
+import (
+	"cmp"
+	"encoding/base64"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/rjnemo/auth/internal/logging"
+)
+
+const (
+	envListenAddr    = "AUTH_LISTEN_ADDR"
+	envLogMode       = "AUTH_LOG_MODE"
+	envEnvironment   = "AUTH_ENV"
+	envSessionSecret = "AUTH_SESSION_SECRET"
+
+	defaultListenAddr  = ":8000"
+	defaultEnvironment = "development"
+)
+
+// Config holds application configuration derived from environment variables.
+type Config struct {
+	ListenAddr    string
+	LogMode       logging.Mode
+	Environment   string
+	SessionSecret []byte
+}
+
+// New loads configuration from environment variables, applying defaults and validation.
+func New() (*Config, error) {
+	listenAddr := cmp.Or(strings.TrimSpace(os.Getenv(envListenAddr)), defaultListenAddr)
+	environment := cmp.Or(strings.TrimSpace(os.Getenv(envEnvironment)), defaultEnvironment)
+	logMode := logging.ModeText
+	if rawMode := strings.TrimSpace(os.Getenv(envLogMode)); rawMode != "" {
+		logMode = logging.ParseMode(rawMode)
+	}
+
+	secretRaw, ok := os.LookupEnv(envSessionSecret)
+	if !ok || strings.TrimSpace(secretRaw) == "" {
+		return nil, fmt.Errorf("missing required configuration: set %s to a base64-encoded secret", envSessionSecret)
+	}
+
+	secret, err := base64.StdEncoding.DecodeString(secretRaw)
+	if err != nil {
+		return nil, fmt.Errorf("invalid %s: %w", envSessionSecret, err)
+	}
+
+	cfg := &Config{
+		ListenAddr:    listenAddr,
+		LogMode:       logMode,
+		Environment:   environment,
+		SessionSecret: secret,
+	}
+
+	return cfg, nil
+}

internal/config/config_test.go

@@ -0,0 +1,82 @@
+package config
+
+import (
+	"encoding/base64"
+	"testing"
+
+	"github.com/rjnemo/auth/internal/logging"
+)
+
+func TestNewDefaults(t *testing.T) {
+	t.Setenv("AUTH_SESSION_SECRET", base64.StdEncoding.EncodeToString(bytesOfLength(32)))
+	cfg, err := New()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if cfg.ListenAddr != ":8000" {
+		t.Fatalf("expected default listen addr, got %s", cfg.ListenAddr)
+	}
+	if cfg.LogMode != logging.ModeText {
+		t.Fatalf("expected default log mode text, got %s", cfg.LogMode)
+	}
+	if cfg.Environment != "development" {
+		t.Fatalf("expected default environment, got %s", cfg.Environment)
+	}
+	if got := len(cfg.SessionSecret); got != 32 {
+		t.Fatalf("expected secret length 32, got %d", got)
+	}
+}
+
+func TestNewOverrides(t *testing.T) {
+	secret := base64.StdEncoding.EncodeToString(bytesOfLength(40))
+	t.Setenv("AUTH_SESSION_SECRET", secret)
+	t.Setenv("AUTH_LISTEN_ADDR", "127.0.0.1:9000")
+	t.Setenv("AUTH_LOG_MODE", "json")
+	t.Setenv("AUTH_ENV", "production")
+
+	cfg, err := New()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if cfg.ListenAddr != "127.0.0.1:9000" {
+		t.Fatalf("expected overridden listen addr, got %s", cfg.ListenAddr)
+	}
+	if cfg.LogMode != logging.ModeJSON {
+		t.Fatalf("expected json mode, got %s", cfg.LogMode)
+	}
+	if cfg.Environment != "production" {
+		t.Fatalf("expected environment production, got %s", cfg.Environment)
+	}
+	if len(cfg.SessionSecret) != 40 {
+		t.Fatalf("expected secret length 40, got %d", len(cfg.SessionSecret))
+	}
+}
+
+func TestNewMissingSecret(t *testing.T) {
+	t.Setenv("AUTH_SESSION_SECRET", "")
+	if _, err := New(); err == nil {
+		t.Fatalf("expected error for missing secret")
+	}
+}
+
+func TestNewInvalidSecret(t *testing.T) {
+	t.Setenv("AUTH_SESSION_SECRET", "not-base64")
+	if _, err := New(); err == nil {
+		t.Fatalf("expected error for invalid secret")
+	}
+}
+
+func TestNewShortSecretAccepted(t *testing.T) {
+	t.Setenv("AUTH_SESSION_SECRET", base64.StdEncoding.EncodeToString(bytesOfLength(16)))
+	if _, err := New(); err != nil {
+		t.Fatalf("expected short secret to pass config load, got %v", err)
+	}
+}
+
+func bytesOfLength(n int) []byte {
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = byte(i % 255)
+	}
+	return b
+}

internal/server/server.go

@@ -2,13 +2,13 @@ package server
 
 import (
 	"context"
-	"crypto/rand"
 	"fmt"
 	"html/template"
 	"io"
 	"log/slog"
 	"time"
 
+	"github.com/rjnemo/auth/internal/config"
 	"github.com/rjnemo/auth/internal/logging"
 	"github.com/rjnemo/auth/internal/service/auth"
 	"github.com/rjnemo/auth/web"
@@ -21,14 +21,15 @@ const (
 
 // Server holds HTTP dependencies for the application.
 type Server struct {
-	templates   *template.Template
-	authService *auth.Service
-	sessions    *SessionStore
-	logger      *slog.Logger
+	templates     *template.Template
+	authService   *auth.Service
+	sessions      *SessionStore
+	logger        *slog.Logger
+	configuration config.Config
 }
 
 // New constructs a Server with parsed templates and default state.
-func New(logger *slog.Logger) (*Server, error) {
+func New(cfg config.Config, logger *slog.Logger) (*Server, error) {
 	tmpl, err := template.ParseFS(
 		web.Templates,
 		"templates/login.html",
@@ -45,12 +46,7 @@ func New(logger *slog.Logger) (*Server, error) {
 		return nil, fmt.Errorf("seed user: %w", err)
 	}
 
-	secret := make([]byte, 32)
-	if _, err := rand.Read(secret); err != nil {
-		return nil, fmt.Errorf("session secret: %w", err)
-	}
-
-	sessionStore, err := NewSessionStore(secret)
+	sessionStore, err := NewSessionStore(cfg.SessionSecret)
 	if err != nil {
 		return nil, fmt.Errorf("session store: %w", err)
 	}
@@ -61,10 +57,11 @@ func New(logger *slog.Logger) (*Server, error) {
 	logger = logger.With(slog.String("service", "http"))
 
 	return &Server{
-		templates:   tmpl,
-		authService: auth.NewService(store),
-		sessions:    sessionStore,
-		logger:      logger,
+		templates:     tmpl,
+		authService:   auth.NewService(store),
+		sessions:      sessionStore,
+		logger:        logger,
+		configuration: cfg,
 	}, nil
 }
 

internal/service/auth/password.go

@@ -12,8 +12,10 @@ import (
 	"unicode/utf8"
 )
 
-const saltLen = 32
-const passwordMinLength = 8
+const (
+	saltLen           = 32
+	passwordMinLength = 8
+)
 
 var ErrWeakPassword = errors.New("auth: password does not meet complexity requirements")