Gets and sets the property CallerReference. A unique number that ensures the request
            can't be replayed.    If the CallerReference is new (no matter the content of the
            CloudFrontOriginAccessIdentityConfig object), a new origin access identity is created.
               If the CallerReference is a value you already sent in a previous request to create
            an identity, and the content of the CloudFrontOriginAccessIdentityConfig is identical
            to the original request (ignoring white space),    the response includes the same
            information returned to the original request.    If the CallerReference is a value
            you already sent in a previous request to create an identity but the content of the
            CloudFrontOriginAccessIdentityConfig is different from the original request,    CloudFront
            returns a CloudFrontOriginAccessIdentityAlreadyExists error.
            
 Declaration Syntax
 Declaration Syntax| C# | 
public string CallerReference { get; set; }