Added email-domain flag to restrict access to given domain (#32)

README.md

@@ -65,20 +65,21 @@ usage: kuberos [<flags>] [<oidc-issuer-url>] [<client-id>] [<client-secret-file>
 Provides OIDC authentication configuration for kubectl.
 
 Flags:
-      --help             Show context-sensitive help (also try --help-long and
-                         --help-man).
+      --help             Show context-sensitive help (also try --help-long and --help-man).
       --listen=":10003"  Address at which to expose HTTP webhook.
   -d, --debug            Run with debug logging.
+      --extra-scopes=EXTRA-SCOPES ...
+                         List of additional scopes to provide in token.
       --shutdown-grace-period=1m
-                         Wait this long for sessions to end before shutting
-                         down.
+                         Wait this long for sessions to end before shutting down.
+      --email-domain=EMAIL-DOMAIN
+                         The email domain to restrict access to.
 
 Args:
   [<oidc-issuer-url>]     OpenID Connect issuer URL.
   [<client-id>]           OAuth2 client ID.
   [<client-secret-file>]  File containing OAuth2 client secret.
-  [<kubecfg-template>]    A kubecfg file containing clusters to populate with a
-                          user and contexts.
+  [<kubecfg-template>]    A kubecfg file containing clusters to populate with a user and contexts.
 ```
 
 The partial `kubeconfig` template should contain only cluster entries and

cmd/kuberos/kuberos.go

@@ -43,10 +43,11 @@ func logRequests(h http.Handler, log *zap.Logger) http.Handler {
 
 func main() {
 	var (
-		app    = kingpin.New(filepath.Base(os.Args[0]), "Provides OIDC authentication configuration for kubectl.").DefaultEnvars()
-		listen = app.Flag("listen", "Address at which to expose HTTP webhook.").Default(":10003").String()
-		debug  = app.Flag("debug", "Run with debug logging.").Short('d').Bool()
-		scopes = app.Flag("scopes", "List of additional scopes to provide in token.").Default("profile", "email").Strings()
+		app         = kingpin.New(filepath.Base(os.Args[0]), "Provides OIDC authentication configuration for kubectl.").DefaultEnvars()
+		listen      = app.Flag("listen", "Address at which to expose HTTP webhook.").Default(":10003").String()
+		debug       = app.Flag("debug", "Run with debug logging.").Short('d').Bool()
+		scopes      = app.Flag("scopes", "List of additional scopes to provide in token.").Default("profile", "email").Strings()
+		emailDomain = app.Flag("email-domain", "The eamil domain to restrict access to.").String()
 
 		grace            = app.Flag("shutdown-grace-period", "Wait this long for sessions to end before shutting down.").Default("1m").Duration()
 		shutdownEndpoint = app.Flag("shutdown-endpoint", "Insecure HTTP endpoint path (e.g., /quitquitquit) that responds to a GET to shut down kuberos.").String()
@@ -81,7 +82,7 @@ func main() {
 		Endpoint:     provider.Endpoint(),
 		Scopes:       sr.Get(),
 	}
-	e, err := extractor.NewOIDC(provider.Verifier(&oidc.Config{ClientID: *clientID}), extractor.Logger(log))
+	e, err := extractor.NewOIDC(provider.Verifier(&oidc.Config{ClientID: *clientID}), extractor.Logger(log), extractor.EmailDomain(*emailDomain))
 	kingpin.FatalIfError(err, "cannot setup OIDC extractor")
 
 	h, err := kuberos.NewHandlers(cfg, e, kuberos.Logger(log))

extractor/oidc.go

@@ -3,6 +3,7 @@ package extractor
 import (
 	"context"
 	"net/http"
+	"strings"
 
 	"go.uber.org/zap"
 	"golang.org/x/oauth2"
@@ -34,9 +35,10 @@ type OIDC interface {
 }
 
 type oidcExtractor struct {
-	log *zap.Logger
-	v   *oidc.IDTokenVerifier
-	h   *http.Client
+	log         *zap.Logger
+	v           *oidc.IDTokenVerifier
+	h           *http.Client
+	emailDomain string
 }
 
 // An Option represents a OIDC extractor option.
@@ -58,6 +60,14 @@ func Logger(l *zap.Logger) Option {
 	}
 }
 
+// EmailDomain adds the given email domain to an OIDC extractor
+func EmailDomain(domain string) Option {
+	return func(o *oidcExtractor) error {
+		o.emailDomain = domain
+		return nil
+	}
+}
+
 // NewOIDC creates a new OIDC extractor.
 func NewOIDC(v *oidc.IDTokenVerifier, oo ...Option) (OIDC, error) {
 	l, err := zap.NewProduction()
@@ -104,5 +114,10 @@ func (o *oidcExtractor) Process(ctx context.Context, cfg *oauth2.Config, code st
 	if err := idt.Claims(params); err != nil {
 		return nil, errors.Wrap(err, "cannot extract claims from ID token")
 	}
+
+	if o.emailDomain != "" && !strings.HasSuffix(params.Username, "@"+o.emailDomain) {
+		return nil, errors.New("Invalid email domain, expecting " + o.emailDomain)
+	}
+
 	return params, nil
 }