Iterate with ng-options in a dictionary(object)

Iterate with ng-options in a dictionary(object)

I need to iterate over the following object with ng-options:
var a = {
'optionName1': 'optionValue1',
'optionName2': 'optionValue2',
'optionName3': 'optionValue3',
'optionName4': 'optionValue4',
};
I get this object in this format from a 3rd party resource, and I'd rather
no to re-arrange it manually.
I already did a Google search, and looked into the documentation, it deals
with lists, and lists of objects only from what I could tell.