Fix reset password endpoint (#2921)

Fixes the admin password reset endpoint.
It was using a wrong variable, so could not detect the user.
Adds some more checks to validate we can actually change the password.

internal/httputil/httpapi.go

@@ -198,7 +198,7 @@ func MakeExternalAPI(metricsName string, f func(*http.Request) util.JSONResponse
 
 // MakeHTMLAPI adds Span metrics to the HTML Handler function
 // This is used to serve HTML alongside JSON error messages
-func MakeHTMLAPI(metricsName string, f func(http.ResponseWriter, *http.Request) *util.JSONResponse) http.Handler {
+func MakeHTMLAPI(metricsName string, enableMetrics bool, f func(http.ResponseWriter, *http.Request) *util.JSONResponse) http.Handler {
 	withSpan := func(w http.ResponseWriter, req *http.Request) {
 		span := opentracing.StartSpan(metricsName)
 		defer span.Finish()
@@ -211,6 +211,10 @@ func MakeHTMLAPI(metricsName string, f func(http.ResponseWriter, *http.Request)
 		}
 	}
 
+	if !enableMetrics {
+		return http.HandlerFunc(withSpan)
+	}
+
 	return promhttp.InstrumentHandlerCounter(
 		promauto.NewCounterVec(
 			prometheus.CounterOpts{

internal/validate.go

@@ -0,0 +1,44 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/util"
+)
+
+const minPasswordLength = 8 // http://matrix.org/docs/spec/client_server/r0.2.0.html#password-based
+
+const maxPasswordLength = 512 // https://github.com/matrix-org/synapse/blob/v0.20.0/synapse/rest/client/v2_alpha/register.py#L161
+
+// ValidatePassword returns an error response if the password is invalid
+func ValidatePassword(password string) *util.JSONResponse {
+	// https://github.com/matrix-org/synapse/blob/v0.20.0/synapse/rest/client/v2_alpha/register.py#L161
+	if len(password) > maxPasswordLength {
+		return &util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON(fmt.Sprintf("password too long: max %d characters", maxPasswordLength)),
+		}
+	} else if len(password) > 0 && len(password) < minPasswordLength {
+		return &util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.WeakPassword(fmt.Sprintf("password too weak: min %d chars", minPasswordLength)),
+		}
+	}
+	return nil
+}