OrderByClauseInUrl contain backing column names leading to failure at Column Authorization stage

[ayush3797]

What is the issue?
While working on this issue : #567 , there were a lot of failures in test cases, one of which was failure of this Test: FindTestWithDifferentMappedFieldsAndOrderBy(), and there are other tests similar to this one.

As it turned out, the request failed in AuthorizationResolver.AreColumnsAllowedForAction() authorization check stage. On closer inspection, I found out that the issue is arising because the RestRequestContext.OrderByClauseInUrl (which is a list of OrderByColumns) has the column names already as backing columns.
(See how the OrderByClause is populated in RequestParser.GenerateOrderByList()).

The expectation in AuthorizationResolver.AreColumnsAllowedForAction() is that the columns argument passed to it has exposedColumnNames, and not backing column names. However the OrderByClauseInUrl has backing column names, which are added to the column IEnum, and hence we don't find a mapping from a backing column name and we get an exception at AuthorizationResolver.AreColumnsAllowedForAction() , Line 143.

[ayush3797]

I executed the test as a request to the runtime, and the request failed. If you look at the config file for MsSql, you will see that the Shrub entity has a mapping from species(backing):fancyName(exposed). But when the code hits the AuthorizationResolver.AreColumnsAllowedForAction() check, the columns argument (which is expected to contain the exposed column names) has species instead of fancyName in it. And we thus get an exception.

[ayush3797]

Continuation of the previous comment, when the exception occured, from the debugger locals:
exposedColumn : species (which is a backingColumn and not exposed column, here is the issue)
columns: ["species", "treeId"] (which should have been ["fancyName", "treeId"]