feat(oidcgate): YAML config loader with env-var overrides

cmd/oidcgate/config.go

@@ -0,0 +1,193 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/lukaszraczylo/traefikoidc"
+	"gopkg.in/yaml.v3"
+)
+
+// Config is the top-level oidcgate configuration. The OIDC subtree maps 1:1
+// onto traefikoidc.Config; the few extra fields configure the daemon itself.
+type Config struct {
+	Listen    string             `json:"listen"`
+	AuthPath  string             `json:"authPath"`
+	StartPath string             `json:"startPath"`
+	OIDC      traefikoidc.Config `json:"-"`
+}
+
+// envScalarFields lists Config field names (within OIDC and top-level)
+// that may be overridden via OIDCGATE_<UPPER_SNAKE_CASE> environment
+// variables. Only scalar strings/ints/bools are supported; nested structs
+// (Redis, SecurityHeaders, DynamicClientRegistration) stay YAML-only.
+var envScalarFields = []string{
+	"Listen", "AuthPath", "StartPath",
+	"ProviderURL", "ClientID", "ClientSecret", "Audience",
+	"CallbackURL", "LogoutURL", "PostLogoutRedirectURI",
+	"SessionEncryptionKey", "CookiePrefix", "CookieDomain",
+	"LogLevel", "RevocationURL", "OIDCEndSessionURL",
+	"UserIdentifierClaim", "GroupClaimName", "RoleClaimName",
+	"ClientAuthMethod", "ClientAssertionPrivateKey",
+	"ClientAssertionKeyPath", "ClientAssertionKeyID", "ClientAssertionAlg",
+	"CACertPath", "CACertPEM",
+}
+
+// Load reads YAML from path, applies env-var overrides, fills defaults,
+// and forces TrustForwardedURI=true so the library honors X-Forwarded-Uri.
+func Load(path string) (*Config, error) {
+	data, err := os.ReadFile(path) //nolint:gosec // path is a trusted operator-supplied config file path
+	if err != nil {
+		return nil, fmt.Errorf("read config: %w", err)
+	}
+
+	// Pass 1: YAML → generic map.
+	var raw map[string]any
+	if err := yaml.Unmarshal(data, &raw); err != nil {
+		return nil, fmt.Errorf("yaml parse: %w", err)
+	}
+
+	// Split the top-level oidcgate-specific keys away from the OIDC subtree.
+	listen, _ := raw["listen"].(string)
+	authPath, _ := raw["authPath"].(string)
+	startPath, _ := raw["startPath"].(string)
+	delete(raw, "listen")
+	delete(raw, "authPath")
+	delete(raw, "startPath")
+
+	// Pass 2: remaining map → JSON → traefikoidc.Config (uses existing json tags).
+	jsonBytes, err := json.Marshal(raw)
+	if err != nil {
+		return nil, fmt.Errorf("yaml→json: %w", err)
+	}
+	var oidcCfg traefikoidc.Config
+	if err := json.Unmarshal(jsonBytes, &oidcCfg); err != nil {
+		return nil, fmt.Errorf("oidc config parse: %w", err)
+	}
+
+	cfg := &Config{
+		Listen:    listen,
+		AuthPath:  authPath,
+		StartPath: startPath,
+		OIDC:      oidcCfg,
+	}
+
+	applyEnvOverrides(cfg)
+	applyDefaults(cfg)
+
+	// Force standalone semantics: trust X-Forwarded-Uri.
+	cfg.OIDC.TrustForwardedURI = true
+	return cfg, nil
+}
+
+// applyEnvOverrides walks the allow-listed scalar fields and replaces any
+// non-empty OIDCGATE_<UPPER_SNAKE_CASE> env var. Field name "ClientID"
+// becomes "OIDCGATE_CLIENT_ID"; "SessionEncryptionKey" becomes
+// "OIDCGATE_SESSION_ENCRYPTION_KEY".
+func applyEnvOverrides(cfg *Config) {
+	for _, field := range envScalarFields {
+		env := os.Getenv("OIDCGATE_" + camelToSnakeUpper(field))
+		if env == "" {
+			continue
+		}
+		setScalarField(cfg, field, env)
+	}
+}
+
+func setScalarField(cfg *Config, field, value string) {
+	switch field {
+	case "Listen":
+		cfg.Listen = value
+	case "AuthPath":
+		cfg.AuthPath = value
+	case "StartPath":
+		cfg.StartPath = value
+	case "ProviderURL":
+		cfg.OIDC.ProviderURL = value
+	case "ClientID":
+		cfg.OIDC.ClientID = value
+	case "ClientSecret":
+		cfg.OIDC.ClientSecret = value
+	case "Audience":
+		cfg.OIDC.Audience = value
+	case "CallbackURL":
+		cfg.OIDC.CallbackURL = value
+	case "LogoutURL":
+		cfg.OIDC.LogoutURL = value
+	case "PostLogoutRedirectURI":
+		cfg.OIDC.PostLogoutRedirectURI = value
+	case "SessionEncryptionKey":
+		cfg.OIDC.SessionEncryptionKey = value
+	case "CookiePrefix":
+		cfg.OIDC.CookiePrefix = value
+	case "CookieDomain":
+		cfg.OIDC.CookieDomain = value
+	case "LogLevel":
+		cfg.OIDC.LogLevel = value
+	case "RevocationURL":
+		cfg.OIDC.RevocationURL = value
+	case "OIDCEndSessionURL":
+		cfg.OIDC.OIDCEndSessionURL = value
+	case "UserIdentifierClaim":
+		cfg.OIDC.UserIdentifierClaim = value
+	case "GroupClaimName":
+		cfg.OIDC.GroupClaimName = value
+	case "RoleClaimName":
+		cfg.OIDC.RoleClaimName = value
+	case "ClientAuthMethod":
+		cfg.OIDC.ClientAuthMethod = value
+	case "ClientAssertionPrivateKey":
+		cfg.OIDC.ClientAssertionPrivateKey = value
+	case "ClientAssertionKeyPath":
+		cfg.OIDC.ClientAssertionKeyPath = value
+	case "ClientAssertionKeyID":
+		cfg.OIDC.ClientAssertionKeyID = value
+	case "ClientAssertionAlg":
+		cfg.OIDC.ClientAssertionAlg = value
+	case "CACertPath":
+		cfg.OIDC.CACertPath = value
+	case "CACertPEM":
+		cfg.OIDC.CACertPEM = value
+	}
+	// strconv reserved for future int/bool fields when added to the allow-list.
+	_ = strconv.Atoi
+}
+
+func applyDefaults(cfg *Config) {
+	if cfg.AuthPath == "" {
+		cfg.AuthPath = "/oauth2/auth"
+	}
+	if cfg.StartPath == "" {
+		cfg.StartPath = "/oauth2/start"
+	}
+}
+
+// camelToSnakeUpper turns "ClientSecret" into "CLIENT_SECRET",
+// "SessionEncryptionKey" into "SESSION_ENCRYPTION_KEY", etc.
+// Multi-letter acronyms keep their grouping: "OIDCEndSessionURL" →
+// "OIDC_END_SESSION_URL", "CACertPEM" → "CA_CERT_PEM".
+func camelToSnakeUpper(s string) string {
+	var b strings.Builder
+	for i, r := range s {
+		if i > 0 && isUpper(r) {
+			prev := rune(s[i-1])
+			next := rune(0)
+			if i+1 < len(s) {
+				next = rune(s[i+1])
+			}
+			if !isUpper(prev) || (next != 0 && !isUpper(next)) {
+				b.WriteByte('_')
+			}
+		}
+		if r >= 'a' && r <= 'z' {
+			r -= 32
+		}
+		b.WriteRune(r)
+	}
+	return b.String()
+}
+
+func isUpper(r rune) bool { return r >= 'A' && r <= 'Z' }