[OAUTH-WG] Updated text for Native Apps

[Chuck Mortimore <[e-mail]>]

Minor updates for section 9 based upon feedback from the list

-cmort

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9.  Native Applications

A native application is a client which is installed and executes on the end-user's device (i.e. desktop application, native mobile application).  Native applications require special consideration related to security, platform capabilities, and overall end-user experience.  The following are examples of how native applications may utilize OAuth:

   o  Initiate an Authorization Request using an external user-agent: The native application can capture the response from the authorization server using a variety of techniques such as the use of a redirection URI identifying a custom URI scheme (registered with the operating system to invoke the native application as handler), manual copy-and-paste, running a local webserver, browser plug-ins, or by providing a redirection URI identifying a server-hosted resource under the native application's control, which in turn makes the response available to the native application.
   o  Initiate an Authorization Request using an embedded user-agent:  The native application obtains the response by directly communicating with the embedded user-agent.  Techniques include monitoring state changes emitted during URL loading, monitoring http headers, accessing the user-agent's cookie jar, etc.

When choosing between launching an external user-agent and an embedding a user-agent, native application developers should consider the following:

   o  External user-agents may improve completion rate as the end-user may already have an active session with the authorization server removing the need to re-authenticate, and provide a familiar user-agent user experience.  The end-user may also rely on extensions or add-ons to assist with authentication (e.g. password managers or 2-factor device reader).
   o  Embedded user-agents may offer an improved end-user flow, as they remove the need to switch context and open new windows.
   o  Embedded user-agents pose a security challenge because end-users are authenticating in an unidentified window without access to the visual protections offered by many user-agents.  Embedded user-agents educate end-user to trust unidentified requests for authentication (making phishing attacks easier to execute).

When choosing between implicit and authorization code grant types, the following should be considered:

   o  Native applications that use the authorization code grant type flow SHOULD do so without client password credentials, due to their inability to keep those credentials confidential.
   o  Native applications that use the implicit grant type may offer optimized performance in some scenarios due to reduced network requests
   o  The implicit grant type does not return a refresh token