//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2020 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// Low-level methods used to implement HTTP Digest authentication

#ifndef OPENVPN_PROXY_HTTPDIGEST_H
#define OPENVPN_PROXY_HTTPDIGEST_H

#include <cstring> // for std::strlen and others
#include <string>

#include <openvpn/crypto/hashstr.hpp>

namespace openvpn {
  namespace HTTPProxy {

    class Digest
    {
    public:
      // calculate H(A1) as per spec
      static std::string calcHA1(DigestFactory& digest_factory,
				 const std::string& alg,
				 const std::string& username,
				 const std::string& realm,
				 const std::string& password,
				 const std::string& nonce,
				 const std::string& cnonce)
      {
	HashString h1(digest_factory, CryptoAlgs::MD5);
	h1.update(username);
	h1.update(':');
	h1.update(realm);
	h1.update(':');
	h1.update(password);
	BufferPtr result = h1.final();

	if (string::strcasecmp(alg, "md5-sess") == 0)
	  {
	    HashString h2(digest_factory, CryptoAlgs::MD5);
	    h2.update(*result);
	    h2.update(':');
	    h2.update(nonce);
	    h2.update(':');
	    h2.update(cnonce);
	    result = h2.final();
	  }
	return render_hex_generic(*result);
      }

      // calculate request-digest/response-digest as per HTTP Digest spec
      static std::string calcResponse(DigestFactory& digest_factory,
				      const std::string& hA1,         // H(A1)
				      const std::string& nonce,       // nonce from server
				      const std::string& nonce_count, // 8 hex digits
				      const std::string& cnonce,      // client nonce
				      const std::string& qop,         // qop-value: "", "auth", "auth-int"
				      const std::string& method,      // method from the request
				      const std::string& digestUri,   // requested URI
				      const std::string& hEntity)     // H(entity body) if qop="auth-int"
      {
	// calculate H(A2)
	HashString h1(digest_factory, CryptoAlgs::MD5);
	h1.update(method);
	h1.update(':');
	h1.update(digestUri);
	if (string::strcasecmp(qop, "auth-int") == 0)
	  {
	    h1.update(':');
	    h1.update(hEntity);
	  }
	const std::string hA2 = h1.final_hex();

	// calculate response
	HashString h2(digest_factory, CryptoAlgs::MD5);
	h2.update(hA1);
	h2.update(':');
	h2.update(nonce);
	h2.update(':');
	if (!qop.empty())
	  {
	    h2.update(nonce_count);
	    h2.update(':');
	    h2.update(cnonce);
	    h2.update(':');
	    h2.update(qop);
	    h2.update(':');
	  }
	h2.update(hA2);
	return h2.final_hex();
      }
    };
  }
}

#endif