The http_request_args WordPress PHP Filter allows you to modify the arguments used in an HTTP request.
Usage
add_filter('http_request_args', 'your_custom_function', 10, 2);
function your_custom_function($parsed_args, $url) {
    // your custom code here
    return $parsed_args;
}
Parameters
- $parsed_args(array): An array of HTTP request arguments.
- $url(string): The request URL.
More information
See WordPress Developer Resources: http_request_args
Examples
Modify user-agent in HTTP request
Change the user-agent for the request.
add_filter('http_request_args', 'change_user_agent', 10, 2);
function change_user_agent($parsed_args, $url) {
    $parsed_args['user-agent'] = 'Your Custom User Agent';
    return $parsed_args;
}
Increase HTTP request timeout
Increase the timeout for a specific request.
add_filter('http_request_args', 'increase_request_timeout', 10, 2);
function increase_request_timeout($parsed_args, $url) {
    if (strpos($url, 'example.com') !== false) {
        $parsed_args['timeout'] = 60;
    }
    return $parsed_args;
}
Disable SSL verification
Disable SSL verification for a specific request.
add_filter('http_request_args', 'disable_ssl_verification', 10, 2);
function disable_ssl_verification($parsed_args, $url) {
    if (strpos($url, 'example.com') !== false) {
        $parsed_args['sslverify'] = false;
    }
    return $parsed_args;
}
Add custom header to HTTP request
Add a custom header to the HTTP request.
add_filter('http_request_args', 'add_custom_header', 10, 2);
function add_custom_header($parsed_args, $url) {
    $parsed_args['headers']['X-Custom-Header'] = 'Your Custom Value';
    return $parsed_args;
}
Block HTTP requests to a specific domain
Prevent requests to a specific domain.
add_filter('http_request_args', 'block_specific_domain', 10, 2);
function block_specific_domain($parsed_args, $url) {
    if (strpos($url, 'baddomain.com') !== false) {
        $parsed_args['blocking'] = false;
    }
    return $parsed_args;
}