Php – The “https://getcomposer.org/versions” file could not be downloaded: SSL operation failed with code 1. OpenSSL Error messages: error: 1416F086

You would know the length if you wrote the XmlTextWriter to something like a MemoryStream first. From there, you could get the bytes, set the httpWebRequest.ContentLength to the length of the byte array, and then write the byte array to your request

edit

The middle of your code would look something like this (I think):

    MemoryStream ms = new MemoryStream();
    using (writer = new XmlTextWriter(ms, System.Text.Encoding.UTF8))
    {
        writePaymentRequest(writer, registrant, amount, signature, ipaddress);
    }
    byte[] bytes = ms.ToArray();
    ms.Close();
    httpWebRequest.GetRequestStream().Write(bytes, 0, bytes.Length);
    httpWebRequest.ContentLength = bytes.Length;

edit #2

Instead of XmlTextWriter(ms, System.Text.Encoding.UTF8), try XmlTextWriter(ms, new UTF8Encoding(false)) to see if that fixes the encoding issue

I found a solution to this

I'm running:
FreeBSD 10.1
Apache2.4
PHP 5.6.3

To find the CA file I ran this command

> locate cacert.pem

Result was:
/usr/local/lib/perl5/site_perl/5.16/Mozilla/CA/cacert.pem

Then open the php.ini file and
change this:

;openssl.cafile=

To this:

openssl.cafile=/usr/local/lib/perl5/site_perl/5.16/Mozilla/CA/cacert.pem

Note: This directive is only available on php 5.6.x

Then restart Apache