sub decode-base64(Str:D $str, Bool:D :$bin = False) {
    my @alpha     = flat 'A'..'Z','a'..'z','0'..'9', '+', '/';
    my %encodings = @alpha.kv.hash.antipairs;
    my $ords := $str.comb(/@alpha/).rotor(4, :partial).map: -> $chunk {
        my $n   = [+] $chunk.map: { (%encodings{$_} || 0) +< ((state $m = 24) -= 6) }
        my $res = (16, 8, 0).map: { $n +> $_ +& 255 }
        slip( $res.head( 3 - ( 4 - $chunk.elems ) ) );
    }
    ?$bin ?? Buf.new($ords || 0) !! $ords
}

my $str = decode-base64("dXNlcm5hbWU6dGhpc2lzbm90bXlwYXNzd29yZA==", :bin).decode;

exit $str eq "username:thisisnotmypassword" ?? 0 !! 1;