To fix wp-admin or wp-login.php redirect loop issue follow below steps.
Step 1. Navigate to wordpress installed directory
Step 2. Edit file “wp-config.php” and paste below code after the “<?php” tag
if (strpos($_SERVER['HTTP_X_FORWARDED_PROTO'], 'https') !== false)
$_SERVER['HTTPS']='on';
Step 3. Save “wp-config.php” file.