Function query_string_to_normalized_map 

pub fn query_string_to_normalized_map(
    query_string: &str,
) -> Result<HashMap<String, Vec<String>>, SignatureError>

Available on crate feature unstable only.

Normalize the query parameters by normalizing the keys and values of each parameter and return a HashMap mapping each key to a vector of values (since it is valid for a query parameters to appear multiple times).

The order of the values matches the order that they appeared in the query string – this is important for SigV4 validation.