my $str = "hello"; # no special chars, 1-127
my $sha256 = Digest::SHA::sha256("abc123"); # bytes 0-255
my $hmac = Digest::SHA::hmac_sha512("a message", "a key"); # bytes 0-255
# edit, the following is mangled by PM's editor, imagine greek letters here:
my $unicode_string = "αβγαabc123"; # unicode chars mixed with lower-ascii
my $buffer = ""; # buffer to concatenate above into and POST them
for($str, $sha256, $hmac, $unicode_string){
  $buffer .= Encode::encode("UTF-8", $_);
}
my $b64 = base64_encode($buffer);
my $HTTPheader = "ABC: $b64";
$ua->POST("aurl" ... $b64 ... $HTTPheader ...);
$ua->GET("aurl" ... $b64 ... $HTTPheader ...);
$ua->POST("aurl" ... $buffer ... $HTTPheader ...);
$ua->GET("aurl" ... $buffer ... $HTTPheader ...);
$ua->GET("aurl" ... $unicode_string ... $HTTPheader ...);