Support Authentication Methods Based on Image Metadata

Operating system images are not homogeneous - they support different authentication methods depending on OS type, included software, configuration, etc. An image provider, such as Glance, can publish image meta-data which describes the authentication types supported for a particular image.

It would be very useful if nova could determine at 'nova boot' time whether enough information has been provided by the request in order to setup one or more remote authentication methods for the requester.