pinvoke.net: Edit: advapi32.CredRead

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@pinvoke=http://pinvoke.net/$$$.htm

Summary: Read the credential (generic, domain, etc) from the windows key ring.

!!!!C# Signature:
            [DllImport("Advapi32.dll", EntryPoint = "CredReadW", CharSet = CharSet.Unicode, SetLastError = true)]
            public static extern bool CredRead(string target, CRED_TYPE type, int reservedFlag,
	                                      [MarshalAs(UnmanagedType.CustomMarshaler, MarshalTypeRef = typeof(CredentialInMarshaler))]out Credential credential);
!!!!VB Signature:
 Declare Function CredRead Lib "advapi32.dll" (TODO) As TODO
!!!!User-Defined Types:
            public enum CRED_TYPE : uint
            {
                GENERIC = 1,
                DOMAIN_PASSWORD = 2,
                DOMAIN_CERTIFICATE = 3,
                DOMAIN_VISIBLE_PASSWORD = 4,
                GENERIC_CERTIFICATE = 5,
                DOMAIN_EXTENDED = 6,
                MAXIMUM = 7,      // Maximum supported cred type
                MAXIMUM_EX = (MAXIMUM + 1000),  // Allow new applications to run on old OSes
            }

public enum CRED_PERSIST : uint
            {
                SESSION = 1,
                LOCAL_MACHINE = 2,
                ENTERPRISE = 3,
            }

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
            public struct CREDENTIAL_ATTRIBUTE
            {
                string Keyword;
                uint Flags;
                uint ValueSize;
                IntPtr Value;
            }

//This type is deliberately not designed to be marshalled.
            public class Credential
            {
                public UInt32 Flags;
                public CRED_TYPE Type;
                public string TargetName;
                public string Comment;
                public System.Runtime.InteropServices.ComTypes.FILETIME LastWritten;
                public byte[] CredentialBlob;
                public CRED_PERSIST Persist;
                public CREDENTIAL_ATTRIBUTE[] Attributes;
                public string TargetAlias;
                public string UserName;
            }

/// <summary>
            /// 
            /// </summary>
            public class CredentialInMarshaler : ICustomMarshaler
            {
                [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
                private class NATIVECREDENTIAL
                {
                    public UInt32 Flags;
                    public CRED_TYPE Type;
                    public string TargetName;
                    public string Comment;
                    public System.Runtime.InteropServices.ComTypes.FILETIME LastWritten;
                    public UInt32 CredentialBlobSize;
                    public IntPtr CredentialBlob;
                    public CRED_PERSIST Persist;
                    public UInt32 AttributeCount;
                    public IntPtr Attributes;
                    public string TargetAlias;
                    public string UserName;
                }

public void CleanUpManagedData(object ManagedObj)
                {
                    // Nothing to do since all data can be garbage collected.
                }

public void CleanUpNativeData(IntPtr pNativeData)
                {
                    if (pNativeData == IntPtr.Zero)
                    {
                        return;
                    }
                    CredFree(pNativeData);
                }

public int GetNativeDataSize()
                {
                    throw new NotImplementedException();
                }

public IntPtr MarshalManagedToNative(object obj)
                {
                    throw new NotImplementedException();
                }

public object MarshalNativeToManaged(IntPtr pNativeData)
                {
                    if (pNativeData == IntPtr.Zero)
                    {
                        return null;
                    }

NATIVECREDENTIAL lRawCredential = (NATIVECREDENTIAL)Marshal.PtrToStructure(pNativeData, typeof(NATIVECREDENTIAL));

Credential lCredential = new Credential()
                    {
                        UserName = lRawCredential.UserName,
                        TargetName = lRawCredential.TargetName,
                        TargetAlias = lRawCredential.TargetAlias,
                        Persist = lRawCredential.Persist,
                        Comment = lRawCredential.Comment,
                        Flags = lRawCredential.Flags,
                        LastWritten = lRawCredential.LastWritten,
                        Type = lRawCredential.Type,
                        CredentialBlob = new byte[lRawCredential.CredentialBlobSize],
                        Attributes = new CREDENTIAL_ATTRIBUTE[lRawCredential.AttributeCount]
                    };

Marshal.Copy(lRawCredential.CredentialBlob, lCredential.CredentialBlob, 0, (int)lRawCredential.CredentialBlobSize);

return lCredential;
                }

public static ICustomMarshaler GetInstance(string cookie)
                {
                    return new CredentialInMarshaler();
                }
            }

!!!!Alternative Managed API:
Do you know one?  Please contribute it!

!!!!Notes:
Attributes are not properly supported at this time.

An alternate approach to this can be found at http://blogs.msdn.com/peerchan/pages/487834.aspx. However as presented that technique requires more manual marshalling and more work for the calling code.

Custom Marshalling provide a self contained and caller transparent solution to this scenario, the returned Credentials object is fully managed without the need to worry about object lifetimes.

!!!!Tips & Tricks:
Use System.Text.Encoding.Unicode.GetString to convert the CredentialBlob into a password string.

!!!!Sample Code:
 
Documentation: CredRead@msdn on MSDN