Prevent startup on empty secret

cmd/budgeteer/main.go

@@ -29,11 +29,14 @@ func main() {
 		panic("couldn't open static files")
 	}
 
+	tokenVerifier, err := jwt.NewTokenVerifier(cfg.SessionSecret)
+	if err != nil {
+		panic("couldn't create token verifier")
+	}
+
 	handler := &server.Handler{
 		Service:             queries,
-		TokenVerifier: &jwt.TokenVerifier{
+		TokenVerifier:       tokenVerifier,
-			Secret: cfg.SessionSecret,
-		},
 		CredentialsVerifier: &bcrypt.Verifier{},
 		StaticFS:            http.FS(static),
 	}

jwt/login.go

@@ -11,8 +11,20 @@ import (
 )
 
 // TokenVerifier verifies Tokens.
-type TokenVerifier struct {
+type tokenVerifier struct {
-	Secret string
+	secret string
+}
+
+var ErrEmptySecret = fmt.Errorf("secret is required")
+
+func NewTokenVerifier(secret string) (*tokenVerifier, error) {
+	if secret == "" {
+		return nil, ErrEmptySecret
+	}
+
+	return &tokenVerifier{
+		secret: secret,
+	}, nil
 }
 
 // Token contains everything to authenticate a user.
@@ -28,7 +40,7 @@ const (
 )
 
 // CreateToken creates a new token from username and name.
-func (tv *TokenVerifier) CreateToken(user *postgres.User) (string, error) {
+func (tv *tokenVerifier) CreateToken(user *postgres.User) (string, error) {
 	token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
 		"usr":  user.Email,
 		"name": user.Name,
@@ -37,7 +49,7 @@ func (tv *TokenVerifier) CreateToken(user *postgres.User) (string, error) {
 	})
 
 	// Generate encoded token and send it as response.
-	t, err := token.SignedString([]byte(tv.Secret))
+	t, err := token.SignedString([]byte(tv.secret))
 	if err != nil {
 		return "", fmt.Errorf("create token: %w", err)
 	}
@@ -52,12 +64,12 @@ var (
 )
 
 // VerifyToken verifys a given string-token.
-func (tv *TokenVerifier) VerifyToken(tokenString string) (budgeteer.Token, error) { //nolint:ireturn
+func (tv *tokenVerifier) VerifyToken(tokenString string) (budgeteer.Token, error) { //nolint:ireturn
 	token, err := jwt.Parse(tokenString, func(token *jwt.Token) (interface{}, error) {
 		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
 			return nil, fmt.Errorf("method '%v': %w", token.Header["alg"], ErrUnexpectedSigningMethod)
 		}
-		return []byte(tv.Secret), nil
+		return []byte(tv.secret), nil
 	})
 	if err != nil {
 		return nil, fmt.Errorf("parse jwt: %w", err)