Today, I am gone to tell you several solutions to post iframe on your website especially if your website is using WordPress with author role user

  1. Create the shortcode

Put this code to your function.php in your child theme:

//function to initialise the iframe elements
add_shortcode( 'iframe' , 'mycustom_shortcode_iframe' );
function mycustom_shortcode_iframe($args, $content) {
    $keys = array("src", "width", "height", "scrolling", "marginwidth", "marginheight", "frameborder");
    $arguments = mycustom_extract_shortcode_arguments($args, $keys);
    return '<iframe ' . $arguments . '></iframe>';
}

function mycustom_extract_shortcode_arguments($args, $keys) {
    $result = "";
    foreach ($keys as $key) {
        if (isset($args[$key])) {
            $result .= $key . '="' . $args[$key] . '" ';
        }
    }
    return $result;
}
//End - the iframe elements

Then put this example

[iframe width="100%" height="325" frameborder="0" scrolling="no" marginheight="0" marginwidth="0" src="https://www.google.com/publicdata/embed?ds=d5bncppjof8f9_&amp;ctype=l&amp;strail=false&amp;bcs=d&amp;nselm=h&amp;met_y=sp_pop_grow&amp;scale_y=lin&amp;ind_y=false&amp;rdim=region&amp;idim=country:IDN:VNM:SGP:PHL:MYS:THA:MMR&amp;ifdim=region&amp;tstart=756144000000&amp;tend=1481990400000&amp;hl=en_US&amp;dl=en&amp;ind=false&amp;xMax=-78.84445062499992&amp;xMin=20.823518125000078&amp;yMax=-46.612215914352305&amp;yMin=52.220622466601796&amp;mapType=t&amp;icfg&amp;iconSize=0.5"]

2. Add function to Author
Add this code to your function.php

function add_theme_caps() {
    // gets the author role
    $role = get_role( 'author' );

    // This only works, because it accesses the class instance.
    // would allow the author to edit others' posts for current theme only
    $role->add_cap( 'unfiltered_html' ); 
}
add_action( 'admin_init', 'add_theme_caps');

you can put your iframe code without any change, but “This is a bad idea and you might as well just give those users “higher” roles as with the “unfiltered_html” permission it is not very hard to duplicate the admin authorization cookies and take control of the site.” – quotes

Which one do you prefer?