I'm not sure it solves your problem, but to create a hash with the keys specified in Perl, you have to quote the keys, as they aren't simple barewords:

    fields      => { 'user[email]' => $login, 'user[password]' => $pas
+sword },
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See perlop for details:

The => operator is a synonym for the comma except that it causes a word on its left to be interpreted as a string if it begins with a letter or underscore and is composed only of letters, digits and underscores.