Function canonical_request_string 

pub fn canonical_request_string(
    method: &str,
    path: &str,
    canonical_query: Option<&str>,
    content_type: Option<&str>,
    body: &[u8],
) -> String

Canonical string assembled by the envelope signing path: METHOD\nPATH\nQUERY\nCONTENT-TYPE\nbody-hex. Both seal and verify reconstruct the same string from the same inputs.