Install a library from a private PyPi within setuptools' extras_require

Question

I'm trying to figure out if it's possible to install a library from a private PyPi within the extras_require of setuptools.setup.

Let's say I have the following extras:

setup(
    ...

    "extras_require": {
        "foo": ["lib1==1.0.0", "lib2==1.0.0", "lib3==1.0.0"]
    },
    ...
)

Now, I'd like to add another dependency (lib4==1.0.0) that I have in my private PyPi, something like this (it's just a POC):

setup(
    ...

    "extras_require": {
        "foo": ["lib1==1.0.0", "lib2==1.0.0", "lib3==1.0.0",
                "lib4==1.0.0 --extra-index-url http://localhost/libraries/"]
    },
    ...
)

Is that possible? If not, can you please tell me how I can address this problem?