Function comma_join 

pub fn comma_join(
    header_name: &str,
    real_value: &str,
    benign_value: &str,
) -> String

Comma-join multiple values into a single header.

Per RFC 7230 §3.2.6, a recipient may combine multiple header fields with the same name into one field-value separated by commas. Header: benign, malicious is semantically equivalent to two separate Header: benign and Header: malicious lines. WAFs that split on the first comma may only inspect benign.