Support multiple Issuers

auth.go

@@ -3,68 +3,125 @@ package main
 import (
 	"context"
 	"errors"
+	"fmt"
 	"net/http"
+	"net/url"
 	"slices"
 	"strings"
 	"time"
 
-	"github.com/coreos/go-oidc/v3/oidc"
-	"github.com/rs/zerolog"
+	"github.com/auth0/go-jwt-middleware/v2/jwks"
 	"github.com/rs/zerolog/log"
+	"gopkg.in/go-jose/go-jose.v2/jwt"
 )
 
 var (
 	errInvalidAuthorizationHeader = errors.New("invalid Authorization header")
 )
 
-type Verifier interface {
-	Verify(ctx context.Context, rawIDToken string) (*oidc.IDToken, error)
+type KeyFunc func(ctx context.Context) (interface{}, error)
+type controller struct {
+	providers map[string]KeyFunc
+	audience  string
+	subjects  []string
 }
 
-// AuthHandler returns a Handler to authenticate requests
-func AuthHandler(subjects []string, verifier Verifier) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		log.Trace().Func(func(e *zerolog.Event) {
-			headers := r.Header.Clone()
-			headers.Del("Authorization")
-			if r.Header.Get("Authorization") != "" {
-				headers.Set("Authorization", "!REMOVED!")
-			}
-			e.Interface("headers", headers)
-		}).Msg("Request details")
-		t := time.Now()
-
-		auth := r.Header.Get("Authorization")
-		jwt, err := parseAuthHeader(auth)
+// NewAuthHandler returns a Handler to authenticate requests
+func NewAuthHandler(audience string, subjects, issuers []string) (RouteMapper, error) {
+	providers := make(map[string]KeyFunc, len(issuers))
+	for _, issuer := range issuers {
+		issuerUrl, err := url.Parse(issuer)
 		if err != nil {
-			w.WriteHeader(http.StatusUnauthorized)
-			_, _ = w.Write([]byte("Forbidden"))
-			log.Info().Err(err).Dur("elappsed_ms", time.Since(t)).Int("status", http.StatusUnauthorized).Msg("Unauthorized")
-			return
+			return nil, err
 		}
 
-		token, err := verifier.Verify(r.Context(), jwt)
+		provider := jwks.NewCachingProvider(issuerUrl, 5*time.Hour)
+		providers[issuer] = provider.KeyFunc
+	}
 
-		if err != nil {
-			w.WriteHeader(http.StatusUnauthorized)
-			_, _ = w.Write([]byte("Forbidden"))
-			log.Info().Err(err).Dur("elappsed_ms", time.Since(t)).Int("status", http.StatusUnauthorized).Msg("Unauthorized")
-			return
-		}
+	c := &controller{
+		providers: providers,
+		audience:  audience,
+		subjects:  subjects,
+	}
+	return func(mux *http.ServeMux) {
+		mux.Handle("/auth", c)
+	}, nil
+}
 
-		subject := token.Subject
-		found := slices.Contains(subjects, subject)
-		if !found {
-			w.WriteHeader(http.StatusForbidden)
-			_, _ = w.Write([]byte("Forbidden"))
-			log.Info().Err(err).Dur("elappsed_ms", time.Since(t)).Int("status", http.StatusForbidden).Str("sub", subject).Msg("Forbidden")
-			return
-		}
+func (c *controller) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	auth := r.Header.Get("Authorization")
+	authHeader, err := parseAuthHeader(auth)
+	if err != nil {
+		w.WriteHeader(http.StatusUnauthorized)
+		_, _ = w.Write([]byte("Unauthorized"))
+		log.Info().Err(err).Msg("Unauthorized: Invalid auth header")
+		return
+	}
+
+	claims, err := c.getClaims(r.Context(), authHeader)
+	if err != nil {
+		w.WriteHeader(http.StatusUnauthorized)
+		_, _ = w.Write([]byte("Unauthorized"))
+		log.Warn().Err(err).Msg("Forbidden: Invalid token")
+		return
+	}
+
+	subject := claims.Subject
+
+	found := slices.Contains(c.subjects, subject)
+	if !found {
+		w.WriteHeader(http.StatusForbidden)
+		_, _ = w.Write([]byte("Forbidden"))
+		log.Warn().Str("sub", subject).Msg("Forbidden")
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write([]byte("OK"))
+	log.Info().Str("sub", subject).Msg("Authorized")
+}
+
+func (c *controller) getClaims(ctx context.Context, authHeader string) (*jwt.Claims, error) {
+	var unsafeClaims jwt.Claims
+	token, err := jwt.ParseSigned(authHeader)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse JWT token: %w", err)
+	}
+	err = token.UnsafeClaimsWithoutVerification(&unsafeClaims)
+	if err != nil {
+		return nil, fmt.Errorf("failed to extract JWT unsafeClaims: %w", err)
+	}
+	var keyId string
+	if len(token.Headers) == 1 {
+		keyId = token.Headers[0].KeyID
+	}
+	if keyId == "" {
+		return nil, fmt.Errorf("failed to find keyId in headers")
+	}
+
+	issuer := unsafeClaims.Issuer
+	keyFunc, ok := c.providers[issuer]
+	if !ok {
+		return nil, fmt.Errorf("unknown issuer: %s", issuer)
+	}
+	key, err := keyFunc(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("error getting the keys from the key func: %w", err)
+	}
+
+	var verifiedClaims jwt.Claims
+	err = token.Claims(key, &verifiedClaims)
+	if err != nil {
+		return nil, fmt.Errorf("failed to verify token unsafeClaims: %w", err)
+	}
+
+	expected := jwt.Expected{Audience: []string{c.audience}}
+	if err = verifiedClaims.Validate(expected); err != nil {
+		return nil, fmt.Errorf("failed to verify token unsafeClaims: %w", err)
+	}
 
-		w.WriteHeader(http.StatusOK)
-		_, _ = w.Write([]byte("OK"))
-		log.Info().Dur("elappsed_ms", time.Since(t)).Int("status", http.StatusOK).Str("sub", subject).Msg("Authorized")
-	})
+	return &verifiedClaims, nil
 }
 
 func parseAuthHeader(authorization string) (string, error) {