indefinite article usage: "a thing of something can be found here" vs. "the thing of something can be found here"

Question

I had an argument with my colleague about the usage of the indefinite article in this sentence:

this system uses OAuth 2 as an authentication scheme, a documentation of the authentication service can be found here:

his argument was that the use of a documentation is wrong because we're talking about a specific one here, and that it should be the documentation

My argument was that we mentioned the documentation for the first time here, and it should be indefinite.

Which one is correct? please provider a reference/evidence if possible.

Answer 1

The choice of definite vs. indefinite is not down to whether this is the first time it's been mentioned, but whether you are referring to a specific thing whose identity is known (see Rule #2 of Definite and Indefinite Articles (a, an, the)). In this case, although you've only just mentioned the documentation, it is a specific thing that you know the identity of, even if the reader doesn't (yet) know of that document.

If there are multiple documentations of the service (not just multiple copies of the same document, but multiple different documents) with the others to be found there, there and there, then a documentation could be correct (though it still would sound strange).

Assuming there is one document that documents the service, then you would use "the documentation".