just for fun I asked ChatGPT to provide code to upload a certificate into an SIM7600G modem and after some tweaking I think it could actually work.

Note: I have not tested below code myself.

#include <SoftwareSerial.h>

SoftwareSerial sim7600gSerial(14, 12); // RX, TX pins for ESP32

const char* ROOT_CERTIFICATE =
  "-----BEGIN CERTIFICATE-----\n" \
  "yrvhNk3cRUBDjAfQ/hp8nQmfQIUpq95CE7Qw8Ty4ekOBL0BtLJjgsL4AqKK1Xf5K\n" \
  "c6kCqKYW4H8xBjJYlFe//KkF1X8tBRR7ZYh3tBpoaiG4IQKerf6DRd1eQ2qBvA7Y\n" \
  "OvG+K/8dLQ7BScscx9fJWxkFtXv+j4I2VpO3F8Z9sQHHlk49xdmMxEi2J1U5JBAu\n" \
  "jyAVhysYtdnE+1p4KhLSWmCU1rlMj54BQrKy38szmR0EzOxZKIZFvywIPkkNcXx2\n" \
  "aa3CzgIKJVf8AhsgthD9Wp6qu1vkxN0tJj2kF4/shtv4/z2Jj4mDN1/0Cg2hOsQQ\n" \
  "0PipV/nMhOF0fu8x7n3P9+q8U6SWANJyvKXh3OLjWhS/iPp89xQaC4xlGzTTvwiE\n" \
  "Zg==\n" \
  "-----END CERTIFICATE-----\n";

void setup() {
  Serial.begin(9600);
  sim7600gSerial.begin(9600);
  delay(1000);

  // Upload the root certificate to the SIM7600G modem
  sim7600gSerial.println("AT+CFUN=1"); // Turn on the modem
  sim7600gSerial.print("AT+CCERTDOWN=\"root_cert.pem\",");
  sim7600gSerial.println(strlen(ROOT_CERTIFICATE)); // Send the length of the certificate data
  sim7600gSerial.print(ROOT_CERTIFICATE);
}

void loop() {
  // do nothing
}

Thanks
Felix

I think an MQTT connection can be done in two (maybe more) ways:

Either by using AT commands to upload the certificates into the modem and the use the built in AT commands for the MQTT connection.

I assume UIFlow takes another route. It is not using the built-in MQTT AT commands, but rather makes plain internet connection and then uses micropython MQTT commands; hence no need to upload the certificates into the modem.

Note: above is just a guess, so I could be wrong.

BTW: I don't think there is a right or wrong way to do it.

Thanks
Felix

What i ended up doing was uploading the certs to the device, then just doing an open() in python, then sent those over UART using AT commands to the modem. Everything is working fine now, but not sure if this is the 'proper' way to do it.