which version of lib curl do you use?

I can not reproduce this error(it works fine with lib curl 7.22.0) here

according to phpinfo(), i have curl version 7.42.1.

i am using php 5.6.11 downloaded from here: 
http://windows.php.net/downloads/releases/php-5.6.11-nts-Win32-VC11-x86.zip

I am experiencing same problem on PHP 5.6.12 x86, cURL 7.42.1, Windows 8.1 x64.
It instead seems to work as expected on my Ubuntu machine (running PHP 5.6.11 and cURL 7.35.0).

On Windows specifically, this seems to be related to the change to using SSPI with  cURL.  curl_sasl_sspi.c adds "Curl_override_sspi_http_realm()" in curl-7.43.0. Going all the way back to php-5.3.29 works (php-5.4 through php-5.5 crash due to the aforementioned bug).  Building my own version of cURL based on 7.43.0 (from [1]) and building it into php-5.6.14 manually works as expected.

Note that this only explains the Windows case of this issue (where Realm is sent back to the server as an empty string).  This can be verified using CURLOPT_VERBOSE = true.

[1] https://github.com/winlibs/cURL

One other note: it seems curl in general is having issues with httpbin's digest test service (I have the same issues with both curl and wget on the command line)... this one seems to work fine (hosted by webdav.org), though it returns a 404:

<?php
$curl = curl_init();

$curl_options = [
	CURLOPT_HTTPAUTH => CURLAUTH_ANY,
	
	#CURLOPT_USERPWD => 'user:passwd',
	#CURLOPT_URL => 'http://httpbin.org/digest-auth/auth/user/passwd',
	CURLOPT_USERPWD => 'user1:user1',
	CURLOPT_URL => 'http://test.webdav.org/auth-digest',
	CURLOPT_HEADER => true,
        CURLOPT_VERBOSE => true
];
curl_setopt_array($curl, $curl_options);

curl_exec($curl);
curl_close($curl);
?>

One last post, with working httpbin.org support (note that they test for the presence of a fake cookie -- instead of setting up a cookie jar, I've just passed back the fake cookie):

<?php
$curl = curl_init();

$curl_options = [
	CURLOPT_HTTPAUTH => CURLAUTH_ANY,
	
	CURLOPT_USERPWD => 'user:passwd',
	CURLOPT_URL => 'http://httpbin.org/digest-auth/auth/user/passwd',
	CURLOPT_HEADER => true,
        CURLOPT_VERBOSE => true,
        CURLOPT_COOKIE => 'fake=fake_value'
];
curl_setopt_array($curl, $curl_options);

curl_exec($curl);
curl_close($curl);
?>

I have the same problem with PHP-clients/scripts and the CalDAV/SabreDAV-framework (also included in Owncloud, Baikal, etc.) on my Apache 2.4.17 (Win32/VC11 from Apachelounge on Win7/64).

I've played a little bit with different versions of the PHP 5.6.x releases and found the following:

php_curl.dll  <= v5.6.4     - no problems
php_curl.dll  v5.6.5/v5.6.6 - crash with Auth_Digest
php_curl.dll  => v5.6.7     - Auth_Digest failed

The bug is also in the PHP 5.5 release and PHP 5.4 (last stable PHP_CURL.DLL I've found in v5.4.36)

I am experiencing same problem now on PHP 7.0.20 x86, Windows x64. 

It instead to work as expected on the same PHP installation, but with the Curl-Lib from PHP 7.0.14.

The given test script works as expected for me with PHP-7.3 using
7.67.0.  Can anybody else still reproduce the reported issue with
any of the supported PHP versions[1] using a somewhat recent
libcurl?

[1] <https://www.php.net/supported-versions.php>

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