install: Update extra-index-url in session from requirements file

Author: Noah Gorny

src/pip/_internal/commands/install.py

@@ -296,6 +296,8 @@ def run(self, options, args):
 
         try:
             reqs = self.get_requirements(args, options, finder, session)
+            # We need to update the auth urls in session
+            session.update_index_urls(finder.index_urls)
 
             warn_deprecated_install_options(
                 reqs, options.install_options

src/pip/_internal/network/session.py

@@ -305,6 +305,14 @@ def __init__(self, *args, **kwargs):
         for host in trusted_hosts:
             self.add_trusted_host(host, suppress_logging=True)
 
+    def update_index_urls(self, new_index_urls):
+        # type: (List[str]) -> None
+        """
+        :param new_index_urls: New index urls to update the authentication
+            handler with.
+        """
+        self.auth.index_urls = new_index_urls
+
     def add_trusted_host(self, host, source=None, suppress_logging=False):
         # type: (str, Optional[str], bool) -> None
         """