DecodeJSONBody Decode request body from JSON to struct copied from https://www.alexedwards.net/blog/how-to-properly-parse-a-json-request-body.

DecodeJSONOrReportError Decodes request JSON and writes possible errors to the ResponseWriter.

NewThrottlingAwareClient Wraps given client and handles retries on HTTP 429.

SendEmptyResponse Marshals empty response into JSON and sends it to the client.

SendErrorResponse Sends error response as required by Firebase SDK.

SendResponse Marshals response into JSON and sends it to the client.