Parse the date header value from the AWS IoT response, and generate the formatted ISO 8601 date required for authentication.

SigV4Status_t SigV4_AwsIotDateToIso8601( const char * pDate,
                                         size_t dateLen,
                                         char * pDateISO8601,
                                         size_t dateISO8601Len );

This is an optional utility function available to the application, to assist with formatting of the date header obtained from AWS IoT (when requesting a temporary token or sending a POST request).

AWS SigV4 authentication requires an ISO 8601 date to be present in the "x-amz-date" request header, as well as in the credential scope (must be identical). For additional information on date handling, please see https://docs.aws.amazon.com/general/latest/gr/sigv4-date-handling.html.

Acceptable Input Formats:

RFC 5322 (ex. "Thu, 18 Jan 2018 09:18:06 GMT"), the preferred format in HTTP 'Date' response headers. If using this format, the date parameter should match "***, DD 'MMM' YYYY hh:mm:ss GMT" exactly.
RFC 3339 (ex. "2018-01-18T09:18:06Z"), found occasionally in 'Date' and expiration headers. If using this format, the date parameter should match "YYYY-MM-DD'T'hh:mm:ss'Z'" exactly.

Formatted Output:

The ISO8601-formatted date will be returned in the form "YYYYMMDD'T'HHMMSS'Z'" (ex. "20180118T091806Z").

Parameters

[in]	pDate	The date header (in RFC 3339 or RFC 5322 formats). An acceptable date header can be found in the HTTP response returned by AWS IoT. This value should use UTC (with no time-zone offset), and be exactly 20 or 29 characters in length (excluding the null character), to comply with RFC 3339 and RFC 5322 formats, respectively.
[in]	dateLen	The length of the pDate header value. Must be either SIGV4_EXPECTED_LEN_RFC_3339 or SIGV4_EXPECTED_LEN_RFC_5322, for valid input parameters.
[out]	pDateISO8601	The formatted ISO8601-compliant date. The date value written to this buffer will be exactly 16 characters in length, to comply with the ISO8601 standard required for SigV4 authentication.
[in]	dateISO8601Len	The length of buffer pDateISO8601. Must be at least SIGV4_ISO_STRING_LEN bytes, for valid input parameters.

Returns: SigV4Success code if successful, error code otherwise.

Example

// The following example shows how to use the SigV4_AwsIotDateToIso8601
// function to convert an AWS IoT date header value to a ISO 8601 date.
 
SigV4Status_t status = SigV4Success;
char pDateISO8601[SIGV4_ISO_STRING_LEN] = {0};
size_t pDateISO8601Len = SIGV4_ISO_STRING_LEN;
 
// pDate and dateLen are the date header and length which are parsed from
// an AWS IoT Credential Provider HTTP response, using an HTTP library.
status = SigV4_AwsIotDateToIso8601( pDate, dateLen, pDateISO8601, pDateISO8601Len );
 
if( status != SigV4Success )
{
   // Failed to parse date
}