It's not clear if you mean consecutive repeating or more than 2 repeats anywhere. If the latter, this might work:

c:\test>p1
{ 
    printf "password: "; 
    chomp( my $pass = <STDIN> ); 
    redo if $pass =~ m[(.).*\1.*\1]; 
    print "'$pass' Ok"; 
    redo 
};;
password: hello
'hello' Ok
password: goodbye
'goodbye' Ok
password: xxx
password: xaxbxc
password:
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