Respect the NETRC environment variable

docs/user/quickstart.rst

@@ -213,7 +213,8 @@ Note: Custom headers are given less precedence than more specific sources of inf
 
 * Authorization headers set with `headers=` will be overridden if credentials
   are specified in ``.netrc``, which in turn will be overridden by the  ``auth=``
-  parameter.
+  parameter. Requests will search for the netrc file at `~/.netrc`, `~/_netrc`,
+  or at the path specified by the `NETRC` environment variable.
 * Authorization headers will be removed if you get redirected off-host.
 * Proxy-Authorization headers will be overridden by proxy credentials provided in the URL.
 * Content-Length headers will be overridden when we can determine the length of the content.

requests/utils.py

@@ -169,14 +169,20 @@ def super_len(o):
 def get_netrc_auth(url, raise_errors=False):
     """Returns the Requests tuple auth for a given url from netrc."""
 
+    netrc_file = os.environ.get('NETRC')
+    if netrc_file is not None:
+        netrc_locations = (netrc_file,)
+    else:
+        netrc_locations = ('~/{}'.format(f) for f in NETRC_FILES)
+
     try:
         from netrc import netrc, NetrcParseError
 
         netrc_path = None
 
-        for f in NETRC_FILES:
+        for f in netrc_locations:
             try:
-                loc = os.path.expanduser('~/{}'.format(f))
+                loc = os.path.expanduser(f)
             except KeyError:
                 # os.path.expanduser can fail when $HOME is undefined and
                 # getpwuid fails. See https://bugs.python.org/issue20164 &