Add config to disable impersonation

Adds gitlab.impersonation_enabled config option defaulting to true to
keep the current default behaviour.

Only the act of impersonation is modified, impersonation token
management is not affected.

1 files changed, 38 insertions, 1 deletions

diff --git a/doc/api/README.md b/doc/api/README.md
index 0e8d1aaf86e..848a6e6b72b 100644
--- a/doc/api/README.md
+++ b/doc/api/README.md
@@ -225,6 +225,43 @@ For more information, refer to the
 Impersonation tokens are used exactly like regular personal access tokens, and can be passed in either the
 `private_token` parameter or the `Private-Token` header.
 
+#### Disable impersonation
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ce/issues/40385) in GitLab
+11.6.
+
+By default, impersonation is enabled. To disable impersonation, GitLab must be
+reconfigured:
+
+**For Omnibus installations**
+
+1. Edit `/etc/gitlab/gitlab.rb`:
+
+    ```ruby
+    gitlab_rails['impersonation_enabled'] = false
+    ```
+
+1. Save the file and [reconfigure](../administration/restart_gitlab.md#omnibus-gitlab-reconfigure)
+   GitLab for the changes to take effect.
+
+To re-enable impersonation, remove this configuration and reconfigure GitLab.
+
+---
+
+**For installations from source**
+
+1. Edit `config/gitlab.yml`:
+
+    ```yaml
+    gitlab:
+      impersonation_enabled: false
+    ```
+
+1. Save the file and [restart](../administration/restart_gitlab.md#installations-from-source)
+   GitLab for the changes to take effect.
+
+To re-enable impersonation, remove this configuration and restart GitLab.
+
 ### Sudo
 
 NOTE: **Note:**
@@ -540,7 +577,7 @@ When you try to access an API URL that does not exist you will receive 404 Not F
 ```
 HTTP/1.1 404 Not Found
 Content-Type: application/json
-{
+{ f
     "error": "404 Not Found"
 }
 ```