How to call an IoT Central https REST API GET operator from an ESP8266

Question

I am currently developing on an ESP8266 in order to interact with the IoT Central devices. I would like to fetch, via HTTPS, telemetry, and parameters of certain Devices from the IoT Central REST API.

However, there are no official or concrete libraries on how to do so (examples, code samples, etc). When using provided examples of Arduino httpClient or ESPWifi libraries, it always generates an error due to the authentication barrier.

The header ''Authorization: SAS Token...'' prior to the GET command also didn't work.

Thanks

Answer 1

Hi,

Use the Postman client for test purpose to see that your GET request will work.

The following screen snippet shows an example for getting a telemetry data:

Note, that the Authorization header is the API token from the IoT Central App.

Thanks
Roman

Answer 2

I tried again with this following logic:

  // wait for WiFi connection  
  if ((WiFiMulti.run() == WL_CONNECTED)) {  
  
    WiFiClient client;  
  
    HTTPClient http;  
  
    Serial.print("[HTTP] begin...\n");  
    if (http.begin(client, "https://....")) {  // HTTP  
      http.setAuthorization("Authorization: SharedAccessSignature sr=7...");  
      http.addHeader(F("Content-Type"), "application/json");        
  
  
      Serial.print("[HTTP] GET...\n");  
      // start connection and send HTTP header  
      int httpCode = http.GET();  
  
      // httpCode will be negative on error  
      if (httpCode > 0) {  
        // HTTP header has been send and Server response header has been handled  
        Serial.printf("[HTTP] GET... code: %d\n", httpCode);  
  
        // file found at server  
        if (httpCode == HTTP_CODE_OK || httpCode == HTTP_CODE_MOVED_PERMANENTLY) {  
          const String& payload = http.getString();  
          Serial.println(payload);  
          Serial.println('DEBUG__________');            
          remoteSwitch = payload;  
        }  
      } else {  
        Serial.printf("[HTTP] GET... failed, error: %s\n", http.errorToString(httpCode).c_str());  
      }  
  
      http.end();  
    } else {  
      Serial.printf("[HTTP} Unable to connect\n");  
    }  
  }  

However, still ended as an error:

Answer 3

Hi,

There is one place I can see that you didn't pass the fingerprint for HTTPS request in line 9, you can follow the discussion here: https://forum.arduino.cc/t/esp8266-httpclient-library-for-https/495245.

You can also try to use the same way "content-type" header to add "Authorization" header.

Hope this will help.

Br,
Johnson