Windows客户端开发--通过CREDENTIAL保存用户名和密码

做windows客户端，尤其是c/s开发，几乎都要接触到用户的登录。需要用户名和密码，那么我们往往要对用户名和密码就行保存。

方案1：写入ini配置文件
用过配置文件保存用户名和密码，密码肯定是不能实明文了，需要采用一定的加密算法。
但是，这是最大的麻烦，就是很容易被破解，反加密，得到用户的密码。
如何读取ini文件，请看：http://blog.csdn.net/wangshubo1989/article/details/47255823

方案2：写入数据口
可以通过写入数据库的方法，比如写入sqlite。
弊端和写入ini大差不差，就是容易被破解。

  std::string last_name;
  bool success = accounts_tb_->Get(kLastUserNameSqlKey, &last_name);
  if (success) 
  {
    if (!last_name.empty()) {
      return last_team_from_cache;
    }
  }

方案3：qt中的QSettings
在qt中，我们可以使用QSettings来保存用户名和密码：

const static QString SETTING_ACCOUNT_ID = "account_id";
QSettings *settings = new QSettings();
settings->setValue(SETTING_ACCOUNT_ID, id);

QString id = settings->value(SETTING_ACCOUNT_ID, "").toString();

方案4：windows系统上的PCREDENTIALW

文件夹：
WinCred.h

PCREDENTIALW介绍：
The CREDENTIAL structure contains an individual credential.
原型：

typedef struct _CREDENTIAL {
  DWORD                 Flags;
  DWORD                 Type;
  LPTSTR                TargetName;
  LPTSTR                Comment;
  FILETIME              LastWritten;
  DWORD                 CredentialBlobSize;
  LPBYTE                CredentialBlob;
  DWORD                 Persist;
  DWORD                 AttributeCount;
  PCREDENTIAL_ATTRIBUTE Attributes;
  LPTSTR                TargetAlias;
  LPTSTR                UserName;
} CREDENTIAL, *PCREDENTIAL;

我们注意关注UserName和CredentialBlob：
CredentialBlob
Secret data for the credential. The CredentialBlob member can be both read and written.

If the Type member is CRED_TYPE_DOMAIN_PASSWORD, this member contains the plaintext Unicode password for UserName. The CredentialBlob and CredentialBlobSize members do not include a trailing zero character. Also, for CRED_TYPE_DOMAIN_PASSWORD, this member can only be read by the authentication packages.
If the Type member is CRED_TYPE_DOMAIN_CERTIFICATE, this member contains the clear test Unicode PIN for UserName. The CredentialBlob and CredentialBlobSize members do not include a trailing zero character. Also, this member can only be read by the authentication packages.
If the Type member is CRED_TYPE_GENERIC, this member is defined by the application.
Credentials are expected to be portable. Applications should ensure that the data in CredentialBlob is portable. The application defines the byte-endian and alignment of the data in CredentialBlob.

UserName
The user name of the account used to connect to TargetName.
If the credential Type is CRED_TYPE_DOMAIN_PASSWORD, this member can be either a DomainName\UserName or a UPN.
If the credential Type is CRED_TYPE_DOMAIN_CERTIFICATE, this member must be a marshaled certificate reference created by calling CredMarshalCredential with a CertCredential.
If the credential Type is CRED_TYPE_GENERIC, this member can be non-NULL, but the credential manager ignores the member.
This member cannot be longer than CRED_MAX_USERNAME_LENGTH (513) characters.

更多的资料去看看msdn:
https://msdn.microsoft.com/en-us/library/windows/desktop/aa374788(v=vs.85).aspx

CredWrite函数
作用：
The CredWrite function creates a new credential or modifies an existing credential in the user’s credential set.
原型：

BOOL CredWrite(
  _In_ PCREDENTIAL Credential,
  _In_ DWORD       Flags
);

CredRead函数
作用：
The CredRead function reads a credential from the user’s credential set.
原型：

BOOL CredRead(
  _In_  LPCTSTR     TargetName,
  _In_  DWORD       Type,
  _In_  DWORD       Flags,
  _Out_ PCREDENTIAL *Credential
);

保存用户名和密码

bool SaveAccount(const std::string& username, const std::string& password) 
{
    char password_chars[255] = { 0 };
    wchar_t username_wstrs[255] = { 0 };
    wchar_t target_name_wstrs[1024] = { 0 };

    // password
    strcpy(password_chars, password.c_str());
    DWORD cbCreds = 1 + strlen(password_chars);

    // username
    std::wstring username_wstr = nbase::UTF8ToUTF16(username);
    wcscpy(username_wstrs, username_wstr.c_str());

    // target name
    std::wstring target_name_wstr = L"MyApp";
    wcscpy(target_name_wstrs, target_name_wstr.c_str());

    CREDENTIALW cred = { 0 };
    cred.Type = CRED_TYPE_GENERIC;
    cred.TargetName = target_name_wstrs;
    cred.CredentialBlobSize = cbCreds;
    cred.CredentialBlob = (LPBYTE)password_chars;
    cred.Persist = CRED_PERSIST_LOCAL_MACHINE;
    cred.UserName = username_wstrs;

    return ::CredWriteW(&cred, 0);
}

读取用户名和密码

bool GetAccount(std::string& username, std::string& password)
{
    wchar_t username_wstrs[255] = { 0 };
    wchar_t target_name_wstrs[1024] = { 0 };

    // target name
    std::wstring target_name_wstr = L"MyApp";

    PCREDENTIALW pcred;

    BOOL success = false;
    do {
        success = ::CredReadW(target_name_wstr.c_str(), CRED_TYPE_GENERIC, 0, &pcred);
        if (!success)
        {
            break;
        }
        username = nbase::UTF16ToUTF8(pcred->UserName);

        std::string pwd((char*)pcred->CredentialBlob, pcred->CredentialBlobSize);
        password = pwd;
        ::CredFree(pcred);
        return true;
    } while (0);

    return false;
}