[git_cl] Add apply_global

Bug: b/351071334
Change-Id: I235eb26cd46a82251b3a757edd37961bce067522
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5719714
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Allen Li <ayatane@chromium.org>

git_cl.py

@@ -3767,6 +3767,14 @@ class GitAuthConfigChanger(object):
         self._apply_sso(cwd)
         self._apply_gitcookies(cwd)
 
+    def apply_global(self, cwd: str) -> None:
+        """Apply config changes to the global (user) Git config.
+
+        This uses the instance's mode as a default for the Gerrit host.
+        """
+        self._apply_global_cred_helper(cwd)
+        self._apply_global_sso(cwd)
+
     def _apply_cred_helper(self, cwd: str) -> None:
         """Apply config changes relating to credential helper."""
         cred_key: str = f'credential.{self._base_url}.helper'
@@ -3810,6 +3818,50 @@ class GitAuthConfigChanger(object):
         else:
             raise TypeError(f'Invalid mode {self.mode!r}')
 
+    def _apply_global_cred_helper(self, cwd: str) -> None:
+        """Apply config changes relating to credential helper."""
+        cred_key: str = f'credential.{self._base_url}.helper'
+        if self.mode == GitConfigMode.NEW_AUTH:
+            self._set_config(cwd, cred_key, '', scope='global', modify_all=True)
+            self._set_config(cwd, cred_key, 'luci', scope='global', append=True)
+        elif self.mode == GitConfigMode.NEW_AUTH_SSO:
+            # Avoid editing the user's config in case they manually
+            # configured something.
+            pass
+        elif self.mode == GitConfigMode.OLD_AUTH:
+            # Avoid editing the user's config in case they manually
+            # configured something.
+            pass
+        else:
+            raise TypeError(f'Invalid mode {self.mode!r}')
+
+    def _apply_global_sso(self, cwd: str) -> None:
+        """Apply config changes relating to SSO."""
+        sso_key: str = f'url.sso://{self._shortname}/.insteadOf'
+        if self.mode == GitConfigMode.NEW_AUTH:
+            # Do not unset protocol.sso.allow because it may be used by other hosts.
+            self._set_config(cwd,
+                             sso_key,
+                             None,
+                             scope='global',
+                             modify_all=True)
+        elif self.mode == GitConfigMode.NEW_AUTH_SSO:
+            self._set_config(cwd,
+                             'protocol.sso.allow',
+                             'always',
+                             scope='global')
+            self._set_config(cwd,
+                             sso_key,
+                             self._base_url,
+                             scope='global',
+                             modify_all=True)
+        elif self.mode == GitConfigMode.OLD_AUTH:
+            # Avoid editing the user's config in case they manually
+            # configured something.
+            pass
+        else:
+            raise TypeError(f'Invalid mode {self.mode!r}')
+
     def _set_config(self, *args, **kwargs) -> None:
         self._set_config_func(*args, **kwargs)