securitycontextprovider.cs

精通SQL Server2005项目开发

#region Copyright & License
//
// Copyright 2001-2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System;

using log4net.Util;

namespace log4net.Core
{
	/// <summary>
	/// The <see cref="SecurityContextProvider"/> providers default <see cref="SecurityContext"/> instances.
	/// </summary>
	/// <remarks>
	/// <para>
	/// A configured component that interacts with potentially protected system
	/// resources uses a <see cref="SecurityContext"/> to provide the elevated
	/// privileges required. If the <see cref="SecurityContext"/> object has
	/// been not been explicitly provided to the component then the component
	/// will request one from this <see cref="SecurityContextProvider"/>.
	/// </para>
	/// <para>
	/// By default the <see cref="SecurityContextProvider.DefaultProvider"/> is
	/// an instance of <see cref="SecurityContextProvider"/> which returns only
	/// <see cref="NullSecurityContext"/> objects. This is a reasonable default
	/// where the privileges required are not know by the system.
	/// </para>
	/// <para>
	/// This default behavior can be overridden by subclassing the <see cref="SecurityContextProvider"/>
	/// and overriding the <see cref="CreateSecurityContext"/> method to return
	/// the desired <see cref="SecurityContext"/> objects. The default provider
	/// can be replaced by programmatically setting the value of the 
	/// <see cref="SecurityContextProvider.DefaultProvider"/> property.
	/// </para>
	/// <para>
	/// An alternative is to use the <c>log4net.Config.SecurityContextProviderAttribute</c>
	/// This attribute can be applied to an assembly in the same way as the
	/// <c>log4net.Config.XmlConfiguratorAttribute"</c>. The attribute takes
	/// the type to use as the <see cref="SecurityContextProvider"/> as an argument.
	/// </para>
	/// </remarks>
	/// <author>Nicko Cadell</author>
	public class SecurityContextProvider
	{
		/// <summary>
		/// The default provider
		/// </summary>
		private static SecurityContextProvider s_defaultProvider = new SecurityContextProvider();

		/// <summary>
		/// Gets or sets the default SecurityContextProvider
		/// </summary>
		/// <value>
		/// The default SecurityContextProvider
		/// </value>
		/// <remarks>
		/// <para>
		/// The default provider is used by configured components that
		/// require a <see cref="SecurityContext"/> and have not had one
		/// given to them.
		/// </para>
		/// <para>
		/// By default this is an instance of <see cref="SecurityContextProvider"/>
		/// that returns <see cref="NullSecurityContext"/> objects.
		/// </para>
		/// <para>
		/// The default provider can be set programmatically by setting
		/// the value of this property to a sub class of <see cref="SecurityContextProvider"/>
		/// that has the desired behavior.
		/// </para>
		/// </remarks>
		public static SecurityContextProvider DefaultProvider
		{
			get { return s_defaultProvider; }
			set { s_defaultProvider = value; }
		}

		/// <summary>
		/// Protected default constructor to allow subclassing
		/// </summary>
		/// <remarks>
		/// <para>
		/// Protected default constructor to allow subclassing
		/// </para>
		/// </remarks>
		protected SecurityContextProvider()
		{
		}

		/// <summary>
		/// Create a SecurityContext for a consumer
		/// </summary>
		/// <param name="consumer">The consumer requesting the SecurityContext</param>
		/// <returns>An impersonation context</returns>
		/// <remarks>
		/// <para>
		/// The default implementation is to return a <see cref="NullSecurityContext"/>.
		/// </para>
		/// <para>
		/// Subclasses should override this method to provide their own
		/// behavior.
		/// </para>
		/// </remarks>
		public virtual SecurityContext CreateSecurityContext(object consumer)
		{
			return NullSecurityContext.Instance;
		}
	}
}