Function canonical_query 

pub fn canonical_query(query: Option<&str>) -> String

query decoded as application/x-www-form-urlencoded, its pairs ordered by key (values of a repeated key keep their order), and re-encoded. None, and a query with no pairs, give "".

Two clients that spell the same query differently (b=2&a=1 and a=1&b=2, %7E and ~) get the same string, so a signature over it survives a proxy or an HTTP library that reorders or re-escapes.