feat: Add firebase auth support and JWT audience check (#71)

internal/serv/internal/auth/auth.go

@@ -32,6 +32,7 @@ type Auth struct {
 		Secret     string
 		PubKeyFile string `mapstructure:"public_key_file"`
 		PubKeyType string `mapstructure:"public_key_type"`
+		Audience   string `mapstructure:"audience"`
 	}
 
 	Header struct {

internal/serv/internal/auth/jwt.go

@@ -2,9 +2,12 @@ package auth
 
 import (
 	"context"
+	"encoding/json"
 	"io/ioutil"
 	"net/http"
+	"strconv"
 	"strings"
+	"time"
 
 	jwt "github.com/dgrijalva/jwt-go"
 	"github.com/dosco/super-graph/core"
@@ -13,8 +16,18 @@ import (
 const (
 	authHeader               = "Authorization"
 	jwtAuth0             int = iota + 1
+	jwtFirebase          int = iota + 2
+	firebasePKEndpoint       = "https://www.googleapis.com/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com"
+	firebaseIssuerPrefix     = "https://securetoken.google.com/"
 )
 
+type firebasePKCache struct {
+	PublicKeys map[string]string
+	Expiration time.Time
+}
+
+var firebasePublicKeys firebasePKCache
+
 func JwtHandler(ac *Auth, next http.Handler) (http.HandlerFunc, error) {
 	var key interface{}
 	var jwtProvider int
@@ -23,6 +36,8 @@ func JwtHandler(ac *Auth, next http.Handler) (http.HandlerFunc, error) {
 
 	if ac.JWT.Provider == "auth0" {
 		jwtProvider = jwtAuth0
+	} else if ac.JWT.Provider == "firebase" {
+		jwtProvider = jwtFirebase
 	}
 
 	secret := ac.JWT.Secret
@@ -56,6 +71,7 @@ func JwtHandler(ac *Auth, next http.Handler) (http.HandlerFunc, error) {
 	}
 
 	return func(w http.ResponseWriter, r *http.Request) {
+
 		var tok string
 
 		if len(cookie) != 0 {
@@ -74,9 +90,16 @@ func JwtHandler(ac *Auth, next http.Handler) (http.HandlerFunc, error) {
 			tok = ah[7:]
 		}
 
-		token, err := jwt.ParseWithClaims(tok, &jwt.StandardClaims{}, func(token *jwt.Token) (interface{}, error) {
+		var keyFunc jwt.Keyfunc
+		if jwtProvider == jwtFirebase {
+			keyFunc = firebaseKeyFunction
+		} else {
+			keyFunc = func(token *jwt.Token) (interface{}, error) {
 				return key, nil
-		})
+			}
+		}
+
+		token, err := jwt.ParseWithClaims(tok, &jwt.StandardClaims{}, keyFunc)
 
 		if err != nil {
 			next.ServeHTTP(w, r)
@@ -86,12 +109,20 @@ func JwtHandler(ac *Auth, next http.Handler) (http.HandlerFunc, error) {
 		if claims, ok := token.Claims.(*jwt.StandardClaims); ok {
 			ctx := r.Context()
 
+			if ac.JWT.Audience != "" && claims.Audience != ac.JWT.Audience {
+				next.ServeHTTP(w, r)
+				return
+			}
+
 			if jwtProvider == jwtAuth0 {
 				sub := strings.Split(claims.Subject, "|")
 				if len(sub) != 2 {
 					ctx = context.WithValue(ctx, core.UserIDProviderKey, sub[0])
 					ctx = context.WithValue(ctx, core.UserIDKey, sub[1])
 				}
+			} else if jwtProvider == jwtFirebase &&
+				claims.Issuer == firebaseIssuerPrefix+ac.JWT.Audience {
+				ctx = context.WithValue(ctx, core.UserIDKey, claims.Subject)
 			} else {
 				ctx = context.WithValue(ctx, core.UserIDKey, claims.Subject)
 			}
@@ -103,3 +134,92 @@ func JwtHandler(ac *Auth, next http.Handler) (http.HandlerFunc, error) {
 		next.ServeHTTP(w, r)
 	}, nil
 }
+
+type firebaseKeyError struct {
+	Err     error
+	Message string
+}
+
+func (e *firebaseKeyError) Error() string {
+	return e.Message + " " + e.Err.Error()
+}
+
+func firebaseKeyFunction(token *jwt.Token) (interface{}, error) {
+	kid, ok := token.Header["kid"]
+
+	if !ok {
+		return nil, &firebaseKeyError{
+			Message: "Error 'kid' header not found in token",
+		}
+	}
+
+	if firebasePublicKeys.Expiration.Before(time.Now()) {
+		resp, err := http.Get(firebasePKEndpoint)
+
+		if err != nil {
+			return nil, &firebaseKeyError{
+				Message: "Error connecting to firebase certificate server",
+				Err:     err,
+			}
+		}
+
+		defer resp.Body.Close()
+
+		data, err := ioutil.ReadAll(resp.Body)
+
+		if err != nil {
+			return nil, &firebaseKeyError{
+				Message: "Error reading firebase certificate server response",
+				Err:     err,
+			}
+		}
+
+		cachePolicy := resp.Header.Get("cache-control")
+		ageIndex := strings.Index(cachePolicy, "max-age=")
+
+		if ageIndex < 0 {
+			return nil, &firebaseKeyError{
+				Message: "Error parsing cache-control header: 'max-age=' not found",
+			}
+		}
+
+		ageToEnd := cachePolicy[ageIndex+8:]
+		endIndex := strings.Index(ageToEnd, ",")
+		if endIndex < 0 {
+			endIndex = len(ageToEnd) - 1
+		}
+		ageString := ageToEnd[:endIndex]
+
+		age, err := strconv.ParseInt(ageString, 10, 64)
+
+		if err != nil {
+			return nil, &firebaseKeyError{
+				Message: "Error parsing max-age cache policy",
+				Err:     err,
+			}
+		}
+
+		expiration := time.Now().Add(time.Duration(time.Duration(age) * time.Second))
+
+		err = json.Unmarshal(data, &firebasePublicKeys.PublicKeys)
+
+		if err != nil {
+			firebasePublicKeys = firebasePKCache{}
+			return nil, &firebaseKeyError{
+				Message: "Error unmarshalling firebase public key json",
+				Err:     err,
+			}
+		}
+
+		firebasePublicKeys.Expiration = expiration
+	}
+
+	if key, found := firebasePublicKeys.PublicKeys[kid.(string)]; found {
+		k, err := jwt.ParseRSAPublicKeyFromPEM([]byte(key))
+		return k, err
+	}
+
+	return nil, &firebaseKeyError{
+		Message: "Error no matching public key for kid supplied in jwt",
+	}
+}