Merge pull request from GHSA-7cc2-r658-7xpf

This fixes a vulnerability with the `CODER_OIDC_EMAIL_DOMAIN` option,
where users with a superset of the allowed email domain would be allowed
to login. For example, given `CODER_OIDC_EMAIL_DOMAIN=google.com`, a
user would be permitted entry if their email domain was
`colin-google.com`.

(cherry picked from commit 4439a920e4)

coderd/userauth.go

@@ -928,15 +928,23 @@ func (api *API) userOIDC(rw http.ResponseWriter, r *http.Request) {
 
 	if len(api.OIDCConfig.EmailDomain) > 0 {
 		ok = false
+		emailSp := strings.Split(email, "@")
+		if len(emailSp) == 1 {
+			httpapi.Write(ctx, rw, http.StatusForbidden, codersdk.Response{
+				Message: fmt.Sprintf("Your email %q is not in domains %q!", email, api.OIDCConfig.EmailDomain),
+			})
+			return
+		}
+		userEmailDomain := emailSp[len(emailSp)-1]
 		for _, domain := range api.OIDCConfig.EmailDomain {
-			if strings.HasSuffix(strings.ToLower(email), strings.ToLower(domain)) {
+			if strings.EqualFold(userEmailDomain, domain) {
 				ok = true
 				break
 			}
 		}
 		if !ok {
 			httpapi.Write(ctx, rw, http.StatusForbidden, codersdk.Response{
-				Message: fmt.Sprintf("Your email %q is not in domains %q !", email, api.OIDCConfig.EmailDomain),
+				Message: fmt.Sprintf("Your email %q is not in domains %q!", email, api.OIDCConfig.EmailDomain),
 			})
 			return
 		}

coderd/userauth_test.go

@@ -757,6 +757,17 @@ func TestUserOIDC(t *testing.T) {
 			"kwc.io",
 		},
 		StatusCode: http.StatusOK,
+	}, {
+		Name: "EmailDomainSubset",
+		IDTokenClaims: jwt.MapClaims{
+			"email":          "colin@gmail.com",
+			"email_verified": true,
+		},
+		AllowSignups: true,
+		EmailDomain: []string{
+			"mail.com",
+		},
+		StatusCode: http.StatusForbidden,
 	}, {
 		Name:          "EmptyClaims",
 		IDTokenClaims: jwt.MapClaims{},