The documentation of Azure Files REST API lists some operations like GET File Metadata where response headers contain an ETag to serve this purpose
The ETag contains a value that you can use to perform operations conditionally, in quotes.
My modified requests with applied 'If-Modified-Since' header were responded by API with HTTP 403.
403 {'date': 'Wed, 05 Aug 2015 13:36:57 GMT', 'content-length': '729', 'content-type': 'application/xml', 'x-ms-request-id': '3cdf88a2-001a-003f-4083-cf9725000000', 'server': 'Microsoft-HTTPAPI/2.0'}
These were the request headers
{'x-ms-version': '2014-02-14', 'Accept-Encoding': 'gzip, deflate', 'Accept': '/', 'User-Agent': 'python-requests/2.5.1 CPython/2.7.6 Linux/3.13.0-61-generic', 'Connection': 'keep-alive', 'If-Modified-Since': 'Tue, 04 Aug 2015 13:36:58 GMT', 'Authorization': 'SharedKey storage_account:secret_key', 'x-ms-date': 'Wed, 05 Aug 2015 13:36:58 GMT'}
Summary: The Azure Files REST API indicated no support for conditional operation, but permitted them. I did not find anything noteable in the documentation of Azure Files REST API.
The documentation for Azure Blob Service contains a section how to apply conditional headers.
Several Blob service operations support the use of conditional headers. You can specify conditional headers to carry out an operation only if a specified condition has been met.
The Blob service follows the HTTP/1.1 protocol specification for conditional headers.
Does Azure File Service REST API support a similar concept of conditional operations?
I have gone through the REST API documentation and as far as I can see, I can say that conditional operations are not supported in File Service in the current version of REST API. They may support it in future version though.