title: Pipenv install fails on cryptography package: "Disabling PEP 517 processing is invalid" error
body: <p>Without being aware of it, I've been using the cryptography package for many months now without issue, but suddenly it won't build and it's brought development on my project to a halt.</p>
  <p>It turns out cryptography is a dependency of one of the other packages in my Pipfile: <code>apns2</code>. As I said, it's been working fine, but something must have changed in my environment. Here is my Pipfile with just that package isolated:</p>
  <pre><code>[[source]]
  url = &quot;https://pypi.python.org/simple&quot;
  verify_ssl = true
  name = &quot;pypi&quot;
  
  [requires]
  python_version = &quot;3.7.9&quot;
  
  [packages]
  
  apns2 = &quot;*&quot;
  
  [dev-packages]
  </code></pre>
  <p>This fails. I use <code>pipenv</code> (the latest version 2020.11.15), so when I run it now this is the output:</p>
  <pre><code># pipenv install
  Creating a virtualenv for this project...
  Pipfile: /Users/dylan/Dev/RideHare/server/Pipfile
  Using /Users/dylan/.pyenv/versions/3.7.9/bin/python3.7m (3.7.9) to create virtualenv...
  ⠏ Creating virtual environment...created virtual environment CPython3.7.9.final.0-64 in 502ms
    creator CPython3Posix(dest=/Users/dylan/.local/share/virtualenvs/server-2uc2X-TS, clear=False, global=False)
    seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/Users/dylan/Library/Application Support/virtualenv)
      added seed packages: pip==20.2.2, setuptools==51.0.0, wheel==0.35.1
    activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator
  
  ✔ Successfully created virtual environment! 
  Virtualenv location: /Users/dylan/.local/share/virtualenvs/server-2uc2X-TS
  Installing dependencies from Pipfile.lock (aa4cd9)...
  An error occurred while installing cryptography==3.3.1; python_version &gt;= '2.7' and python_version not in '3.0, 3.1, 3.2, 3.3, 3.4, 3.5' --hash=sha256:84ef7a0c10c24a7773163f917f1cb6b4444597efd505a8aed0a22e8c4780f27e --hash=sha256:788a3c9942df5e4371c199d10383f44a105d67d401fb4304178020142f020244 --hash=sha256:9f6b0492d111b43de5f70052e24c1f0951cb9e6022188ebcb1cc3a3d301469b0 --hash=sha256:a69bd3c68b98298f490e84519b954335154917eaab52cf582fa2c5c7efc6e812 --hash=sha256:b4890d5fb9b7a23e3bf8abf5a8a7da8e228f1e97dc96b30b95685df840b6914a --hash=sha256:0003a52a123602e1acee177dc90dd201f9bb1e73f24a070db7d36c588e8f5c7d --hash=sha256:7e177e4bea2de937a584b13645cab32f25e3d96fc0bc4a4cf99c27dc77682be6 --hash=sha256:dc42f645f8f3a489c3dd416730a514e7a91a59510ddaadc09d04224c098d3302 --hash=sha256:69e836c9e5ff4373ce6d3ab311c1a2eed274793083858d3cd4c7d12ce20d5f9c --hash=sha256:9e21301f7a1e7c03dbea73e8602905a4ebba641547a462b26dd03451e5769e7c --hash=sha256:0e85aaae861d0485eb5a79d33226dd6248d2a9f133b81532c8f5aae37de10ff7 --hash=sha256:c366df0401d1ec4e548bebe8f91d55ebcc0ec3137900d214dd7aac8427ef3030 --hash=sha256:594a1db4511bc4d960571536abe21b4e5c3003e8750ab8365fafce71c5d86901 --hash=sha256:83d9d2dfec70364a74f4e7c70ad04d3ca2e6a08b703606993407bf46b97868c5! Will try again.
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  Installing initially failed dependencies...
  [InstallError]:   File &quot;/usr/local/Cellar/pipenv/2020.11.15/libexec/lib/python3.9/site-packages/pipenv/cli/command.py&quot;, line 233, in install
  [InstallError]:       retcode = do_install(
  [InstallError]:   File &quot;/usr/local/Cellar/pipenv/2020.11.15/libexec/lib/python3.9/site-packages/pipenv/core.py&quot;, line 2052, in do_install
  [InstallError]:       do_init(
  [InstallError]:   File &quot;/usr/local/Cellar/pipenv/2020.11.15/libexec/lib/python3.9/site-packages/pipenv/core.py&quot;, line 1304, in do_init
  [InstallError]:       do_install_dependencies(
  [InstallError]:   File &quot;/usr/local/Cellar/pipenv/2020.11.15/libexec/lib/python3.9/site-packages/pipenv/core.py&quot;, line 899, in do_install_dependencies
  [InstallError]:       batch_install(
  [InstallError]:   File &quot;/usr/local/Cellar/pipenv/2020.11.15/libexec/lib/python3.9/site-packages/pipenv/core.py&quot;, line 796, in batch_install
  [InstallError]:       _cleanup_procs(procs, failed_deps_queue, retry=retry)
  [InstallError]:   File &quot;/usr/local/Cellar/pipenv/2020.11.15/libexec/lib/python3.9/site-packages/pipenv/core.py&quot;, line 703, in _cleanup_procs
  [InstallError]:       raise exceptions.InstallError(c.dep.name, extra=err_lines)
  [pipenv.exceptions.InstallError]: Looking in indexes: https://pypi.python.org/simple
  [pipenv.exceptions.InstallError]: Collecting cryptography==3.3.1
  [pipenv.exceptions.InstallError]:   Using cached cryptography-3.3.1.tar.gz (539 kB)
  [pipenv.exceptions.InstallError]: ERROR: Disabling PEP 517 processing is invalid: project specifies a build backend of setuptools.build_meta in pyproject.toml
  ERROR: Couldn't install package: cryptography
   Package installation failed...
    ☤  ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉ 0/1 — 00:00:01
  </code></pre>
  <p>If instead of the apns2 line in the Pipfile I substitute cryptography explicitly (crytography = &quot;*&quot;), it fails too in the same way.</p>