Add bare bones user API (#1127)

* Add bare bones user API

with tests!

* linting

userapi/api/api.go

@@ -0,0 +1,38 @@
+// Copyright 2020 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 api
+
+import "context"
+
+// UserInternalAPI is the internal API for information about users and devices.
+type UserInternalAPI interface {
+	QueryProfile(ctx context.Context, req *QueryProfileRequest, res *QueryProfileResponse) error
+}
+
+// QueryProfileRequest is the request for QueryProfile
+type QueryProfileRequest struct {
+	// The user ID to query
+	UserID string
+}
+
+// QueryProfileResponse is the response for QueryProfile
+type QueryProfileResponse struct {
+	// True if the user has been created. Querying for a profile does not create them.
+	UserExists bool
+	// The current display name if set.
+	DisplayName string
+	// The current avatar URL if set.
+	AvatarURL string
+}