var sign = function()

in packages/aws-appsync-auth-link/src/signer/signer.ts [225:277]
41 lines of code
4 McCabe index (conditional complexity)

var sign = function (request, access_info, service_info = null) {
    request.headers = request.headers || {};

    // datetime string and date string
    var dt = new Date(),
        dt_str = dt.toISOString().replace(/[:-]|\.\d{3}/g, ''),
        d_str = dt_str.substr(0, 8),
        algorithm = 'AWS4-HMAC-SHA256';

    var url_info = url.parse(request.url)
    request.headers['host'] = url_info.host;
    request.headers['x-amz-date'] = dt_str;
    if (access_info.session_token) {
        request.headers['X-Amz-Security-Token'] = access_info.session_token;
    }

    // Task 1: Create a Canonical Request
    var request_str = canonical_request(request);

    // Task 2: Create a String to Sign
    service_info = service_info || parse_service_info(request);
    var scope = credential_scope(
        d_str,
        service_info.region,
        service_info.service
    );
    var str_to_sign = string_to_sign(
        algorithm,
        request_str,
        dt_str,
        scope
    );

    // Task 3: Calculate the Signature
    var signing_key = get_signing_key(
        access_info.secret_key,
        d_str,
        service_info
    ),
        signature = get_signature(signing_key, str_to_sign);

    // Task 4: Adding the Signing information to the Request
    var authorization_header = get_authorization_header(
        algorithm,
        access_info.access_key,
        scope,
        signed_headers(request.headers),
        signature
    );
    request.headers['Authorization'] = authorization_header;

    return request;
};