From bd99aa360bcebf9bf2a297939b67922c09062d96 Mon Sep 17 00:00:00 2001
From: Kenneth Reitz <me@kennethreitz.org>
Date: Mon, 11 Sep 2017 10:55:46 -0400
Subject: [PATCH] PIPENV_PIP_INSTALL_FLAGS

Signed-off-by: Kenneth Reitz <me@kennethreitz.org>
---
 pipenv/cli.py          | 7 ++++---
 pipenv/environments.py | 3 +++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/pipenv/cli.py b/pipenv/cli.py
index abfa6900..92dbcd5a 100644
--- a/pipenv/cli.py
+++ b/pipenv/cli.py
@@ -33,7 +33,7 @@ from . import pep508checker, progress
 from .environments import (
     PIPENV_COLORBLIND, PIPENV_NOSPIN, PIPENV_SHELL_COMPAT,
     PIPENV_VENV_IN_PROJECT, PIPENV_USE_SYSTEM, PIPENV_TIMEOUT,
-    PIPENV_SKIP_VALIDATION
+    PIPENV_SKIP_VALIDATION, PIPENV_PIP_INSTALL_FLAGS
 )
 
 # Backport required for earlier versions of Python.
@@ -791,11 +791,12 @@ def pip_install(
 
         no_deps = '--no-deps' if no_deps else ''
 
-        pip_command = '"{0}" install {3} {1} -i {2} --exists-action w'.format(
+        pip_command = '"{0}" install {3} {1} -i {2} --exists-action w {4}'.format(
             which_pip(allow_global=allow_global),
             install_reqs,
             source['url'],
-            no_deps
+            no_deps,
+            PIPENV_PIP_INSTALL_FLAGS or ''
         )
 
         if verbose:
diff --git a/pipenv/environments.py b/pipenv/environments.py
index bf0baddc..eb1b19ac 100644
--- a/pipenv/environments.py
+++ b/pipenv/environments.py
@@ -39,5 +39,8 @@ if PIPENV_VENV_IN_PROJECT:
 if os.name == 'nt':
     PIPENV_NOSPIN = True
 
+# Tells pip to pass extra stuff to $ pip install.
+PIPENV_PIP_INSTALL_FLAGS = os.environ.get('PIPENV_PIP_INSTALL_FLAGS')
+
 # Tells pipenv how long to wait for virtualenvs to be created in seconds
 PIPENV_TIMEOUT = int(os.environ.get('PIPENV_TIMEOUT', 120))