HttpClient: Add cookie support (cookie jar)

[mattsches1]

This is a proposal to add cookie support in HttpClient. With this modification, the client is able to receive and store cookies and automatically send them in a subsequent request, if applicable as per Domain and Path attributes. Receiving multiple cookies in the same response (multiple set-cookie headers) is supported.

Cookie expiry (Expiresand Max-Age attributes) is respected, but relies on RTC to be set properly.

Secure is respected, HttpOnly is stored, but not used anywhere.

See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie for a description of cookie attributes.

This proposal probably has room for additions, code style improvements whatsoever. I created this because I needed to handle cookies when dealing with AWS requests and thought others might have use for it. I tried my best to avoid memory leaks or other negative side effects. But I'm not a professional, and it would for sure be useful if others checked a bit upon possible weak spots.

Usage in addition to standard HttpClient handling):

Declare a cookie jar in the calling instance:
CookieJar cookie_jar;

Before beginning the HTTP request, set

    WiFiClientSecure *client = new WiFiClientSecure;

    if(client) {
        client->setCACert(cert);
        {
            // Add a scoping block for HTTPClient https to make sure it is destroyed before WiFiClientSecure *client is 
            HTTPClient https;

            https.setCookieJar(&cookie_jar);

            }
            if (https.begin(*client, url)) {
            ...

That's it.

The cookie jar is a vector of structs that holds all the cookies of the client and can be used for all requests.

The pull request includes concatenation of received headers, as already proposed in https://github.com/espressif/arduino-esp32/pull/6183. The latter is not required for the cookie jar to work and has only been included since I had mistakenly been working on the master branch of my fork for the former. Sorry for this.

[me-no-dev]

Very nice implementation. I will only suggest that you comment out the code for multiple headers with a note to be uncommented in the future if requests for it come.

[mattsches1]

Done.