file_get_contents can do a POST, create a context for that first:

<?php

$opts = array('http' =>
  array(
    'method'  => 'POST',
    'header'  => "Content-Type: text/xml\r\n".
      "Authorization: Basic ".base64_encode("$https_user:$https_password")."\r\n",
    'content' => $body,
    'timeout' => 60
  )
);
                        
$context  = stream_context_create($opts);
$url = 'https://'.$https_server;
$result = file_get_contents($url, false, $context, -1, 40000);

?>

If doing a negative offset to grab the end of a file and the file is shorter than the offset, then file_get_contents( ) will return false.

If you want it to just return what is available when the file is shorter than the negative offset, you could try again.

For example...

$contents = file_get_contents( $log_file, false, null, -4096 ); // Get last 4KB

if ( false === $contents ) {
    // Maybe error, or maybe file less than 4KB in size.

    $contents = file_get_contents( $log_file, false, null );

    if ( false === $contents ) {
        // Handle real error.
    }
}

To prevent mixed content most browsers/functions will use the protocol already used if you specify only // instead of http:// or https://. This is not the case with file_get_contents. You must specify the protocol. 

This does not work:
<?php
$jsonData = file_get_contents('//example.com/file.json');
print $jsonData;
?>

Specifying only 'example.com/file.json' without the double slash does not work either.

When running on Apache 2.4 , using $_SERVER['REQUEST_SCHEME'] is a better way to be protocol agnostic.
<?php
$jsonData = file_get_contents($_SERVER['REQUEST_SCHEME'].'://example.com/file.json');
print $jsonData;
?>

If using another web server, you may have to get the protocol another way or hard code it.