ESP8266, how to make post request with graphQL - api

Question

I am very new to programming with ESP8266 and can't get this to work.
I am successfully connected to the internet.
With the <ESP8266HTTPClient.h> I am writing the following code:
void loop() {
if (WiFi.status() == WL_CONNECTED) { //Check WiFi connection status
HTTPClient http; //Declare object of class HTTPClient
http.begin("https://api.entur.io/journey-planner/v2/graphql"); //Specify request destination
http.addHeader("Content-Type", "application/json"); //Specify content-type header
http.addHeader("ET-Client-Name", "student-bussAPI"); //Identification requested by the API
int httpCode = http.POST("{\"query\":\"{authorities{id}}\"}"); //Send the request
String payload = http.getString(); //Get the response payload
Serial.println(httpCode); //Print HTTP return code
Serial.println(payload); //Print request response payload
http.end(); //Close connection
} else {
Serial.println("Error in WiFi connection");
}
delay(30000); //Send a request every 30 seconds
}
the code runs with serial output -1
I have tested the query request on postman, and it worked fine there.

Answer 1

The "-1" you are getting is caused by the attempt to establish a connection to a strictly HTTPS service via HTTP.
As the code examples in the ESP8266HttpClient library explain, "httpCode will be negative on error" - what you are seeing is the printing of a http status code of -1.
The easiest way to achieve what you are trying to do here (Query a HTTPS API via the ESP8266httpClient library) would be to connect to it using the current SHA-1 fingerprint of the certificate used by the service as a second parameter of your call to "http.begin".
Example to answer your specific question:
HTTPClient http; //Declare object of class HTTPClient
const char* host = "https://api.entur.io/journey-planner/v2/graphql";
const char* fingerprint ="Current sha-1 fingerprint goes here";
http.begin(host, fingerprint); //Specify request destination and fingerprint for cert to make it do HTTPS
http.addHeader("Content-Type", "application/graphql"); //Content type here is important; Its not JSON
http.addHeader("ET-Client-Name", "Esp8266-BitBrb");
I should also mention that the specific API you are using here has a strict check on content type, so you should change your header to match the data type the API accepts, "application/graphql", or else you'll have trouble :)
Incidentally, i have the full code from a project i did last year with the same service you are using (Hi, fellow Norwegian and EnTur user) available here: https://www.bitbrb.com/electronics/graphql-querying-a-bus
I see they got a new certificate earlier this year, other than that you should be able to cut and paste.
good luck :)