Function sign 

pub fn sign(
    message: &impl ComponentSource,
    components: &[Component],
    params: &SignatureParams,
    label: &str,
    signing_key: &SigningKey,
) -> Result<SignedSignature, HttpSigError>

Signs request over components, producing Signature-Input and Signature field values under label.

Errors

Returns HttpSigError::MissingComponent if a covered header is absent.