did you tried curl2lwp page?

I get (selecting LWP::UserAgent as User-Agent module):

#!perl
use strict;
use warnings;

use LWP::UserAgent;

my $ua = LWP::UserAgent->new( 'send_te' => '0' );
my $r  = HTTP::Request->new(
    'POST' => 'https://login.microsoftonline.com/[TENANT_ID]/oauth2/to
+ken',
    [
        'Accept'         => '*/*',
        'User-Agent'     => 'curl/7.55.1',
        'Content-Length' => '120',
        'Content-Type'   => 'application/x-www-form-urlencoded'
    ],
"grant_type=client_credentials&client_id=[APP_ID]&client_secret=[PASSW
+ORD]&resource=https\x253A\x252F\x252Fmanagement.azure.com\x252F"
);
my $res = $ua->request( $r, );
[download]

L*