ios 中使用https的知识

先看文章，这篇文章说的是使用AFNetworing进行https时的事项，十分好！http://blog.cnbang.net/tech/2416/

ios中使用https，主要就是使用NSURLCredential，先看些必要的官方文档：

NSURLCredential is an immutable object representing an authentication credential consisting of authentication information specific to the type of credential and the type of persistent storage to use, if any.

The URL loading system supports three types of credentials: password-based user credentials, certificate-based user credentials, and certificate-based server credentials (used when verifying the server’s identity).

When you create a credential, you can specify that it should be used for a single request, persisted temporarily (until your app quits), or persisted permanently (in the keychain).

虽然credentials 有许多种，但是针对URL来说，只有3种！

因此有3个初始化方法：

+ credentialForTrust:
+ credentialWithUser:password:persistence:
+ credentialWithIdentity:certificates:persistence:

另外，要参看URL Session Programming Guide中的认证部分：

To attempt to authenticate, the application should create an NSURLCredential object with authentication information of the form expected by the server. You can determine the server’s authentication method by calling authenticationMethod on the protection space of the provided authentication challenge. Some authentication methods supported by NSURLCredential are:

HTTP basic authentication (NSURLAuthenticationMethodHTTPBasic) requires a user name and password. Prompt the user for the necessary information and create an NSURLCredential object with credentialWithUser:password:persistence:.

HTTP digest authentication (NSURLAuthenticationMethodHTTPDigest), like basic authentication, requires a user name and password. (The digest is generated automatically.) Prompt the user for the necessary information and create an NSURLCredential object with credentialWithUser:password:persistence:.

Client certificate authentication (NSURLAuthenticationMethodClientCertificate) requires the system identity and all certificates needed to authenticate with the server. Create an NSURLCredential object with credentialWithIdentity:certificates:persistence:.

Server trust authentication (NSURLAuthenticationMethodServerTrust) requires a trust provided by the protection space of the authentication challenge. Create an NSURLCredential object with credentialForTrust:.
After you’ve created the NSURLCredential object:

For NSURLSession, pass the object to the authentication challenge’s sender using the provided completion handler block.
For NSURLConnection and NSURLDownload, pass the object to the authentication challenge’s sender with useCredential:forAuthenticationChallenge:.