Arduino_HttpClient_ESP8266_AT is an Arduino HTTP client library to be used with ESP-WROOM-02, which is sometimes referred to as ESP8266, through the AT command interface.
This library is made to be usable even with Arduino UNO. It has very limited memory resource, works on different voltage level (5.0V) from ESP8266's 3.3V, and has only one hardware serial. Which means that you can use any kind of Arduino boards with this library without modifying default serial buffer size. It works fine with just 64 byte buffer size, using SoftwareSerial or HardwareSerial, whichever you like.
To be usable for Arduino UNO without serial communication's parity check, we abandoned to receive data from servers. HTTP POST and even HTTP GET can only be used to SEND data.
Please see the following simple and yet sufficient examples.