Gerrit Code Review - Single Sign-On Security

Gerrit supports integration with some types of single sign-on security solutions, making it possible for end-users to setup and manage accounts, without administrator involvement.

OpenID

By default a new Gerrit installation relies upon OpenID to perform user authentication services. To enable OpenID, the auth.type setting should be OpenID:

  git config --file $site_path/etc/gerrit.config auth.type OpenID

As this is the default setting there is nothing required from the site administrator to make use of the OpenID authentication services.

openid.net

If Jetty is being used, you may need to increase the header buffer size parameter, due to very long header lines. Add the following to $JETTY_HOME/etc/jetty.xml under org.mortbay.jetty.nio.SelectChannelConnector:

  <Set name="headerBufferSize">16384</Set>

In order to use permissions beyond those granted to the Anonymous Users and Registered Users groups, an account must only have OpenIDs which match at least one pattern from the auth.trustedOpenID list in gerrit.config. Patterns may be either a standard Java regular expression (java.util.regex) (must start with ^ and end with $) or be a simple prefix (any other string).

Out of the box Gerrit is configured to trust two patterns, which will match any OpenID provider on the Internet:

http:// — trust all OpenID providers using the HTTP protocol
https:// — trust all OpenID providers using the HTTPS protocol

To trust only Yahoo!:

  git config --file $site_path/etc/gerrit.config auth.trustedOpenID https://me.yahoo.com

Database Schema

User identities obtained from OpenID providers are stored as external IDs.

Multiple Identities

Users may link more than one OpenID identity to the same Gerrit account, making it easier for their browser to sign in to Gerrit if they are frequently switching between different unique OpenID accounts.

Warning

Users wishing to link an alternative identity should NOT log in separately with that identity. Doing so will result in a new account being created, and subsequent attempts to link that account with the existing account will fail. In cases where this happens, the administrator will need to manually merge the accounts. See Merging Gerrit User Accounts on the Gerrit Wiki for details.

Linking another identity is also useful for users whose primary OpenID provider shuts down. For example Google shut down their OpenID service on 20th April 2015. Users who failed to add an alternative identity with another OpenID provider before that date will end up with their account only having a disabled Google identity. After creating a separate account with an alternative provider, they will need to ask the administrator to merge the accounts using the previously mentioned method.

To link another identity to an existing account:

Login with the existing account
Select menu Settings → Identities
Click the 'Link Another Identity' button
Select the OpenID provider for the other identity
Authenticate with the other identity

HTTP Basic Authentication

When using HTTP authentication, Gerrit assumes that the servlet container or the frontend web server has performed all user authentication prior to handing the request off to Gerrit.

As a result of this assumption, Gerrit can assume that any and all requests have already been authenticated. The "Sign In" and "Sign Out" links are therefore not displayed in the web UI.

To enable this form of authentication:

  git config --file $site_path/etc/gerrit.config auth.type HTTP
  git config --file $site_path/etc/gerrit.config --unset auth.httpHeader
  git config --file $site_path/etc/gerrit.config auth.emailFormat '{0}@example.com'

The auth.type must always be HTTP, indicating the user identity will be obtained from the HTTP authorization data.

The auth.httpHeader must always be unset. If set to any value (including Authorization) then Gerrit won’t correctly honor the standard Authorization HTTP header.

The auth.emailFormat field ('optional') sets the preferred email address during first login. Gerrit will replace {0} with the username, as obtained from the Authorization header. A format such as shown in the example would be typical, to add the domain name of the organization.

If Apache HTTPd is being used as the primary web server and the Apache server will be handling user authentication, a configuration such as the following is recommended to ensure Apache performs the authentication at the proper time:

  <Location "/login/">
    AuthType Basic
    AuthName "Gerrit Code Review"
    Require valid-user
    ...
  </Location>

Database Schema

User identities are stored as external IDs with "gerrit" as scheme. The user string obtained from the authorization header is stored as ID of the external ID.

Computer Associates Siteminder

Siteminder is a commercial single sign on solution marketed by Computer Associates. It is very common in larger enterprise environments.

When using Siteminder, Gerrit assumes it has been installed in a servlet container which is running behind an Apache web server, and that the Siteminder authentication module has been configured within Apache to protect the entire Gerrit application. In this configuration all users must authenticate with Siteminder before they can access any resource on Gerrit.

As a result of this assumption, Gerrit can assume that any and all requests have already been authenticated. The "Sign In" and "Sign Out" links are therefore not displayed in the web UI.

To enable this form of authentication:

  git config --file $site_path/etc/gerrit.config auth.type HTTP
  git config --file $site_path/etc/gerrit.config auth.httpHeader SM_USER
  git config --file $site_path/etc/gerrit.config auth.emailFormat '{0}@example.com'

The auth.type must always be HTTP, indicating the user identity will be obtained from the HTTP authorization data.

The auth.httpHeader indicates in which HTTP header field the Siteminder product has stored the username. Usually this is "SM_USER", but may differ in your environment. Please refer to your organization’s single sign-on or security group to ensure the setting is correct.

The auth.emailFormat field ('optional') sets the user’s preferred email address when they first login. Gerrit will replace {0} with the username, as supplied by Siteminder. A format such as shown in the example would be typical, to add the domain name of the organization.

  <Set name="headerBufferSize">16384</Set>

Database Schema

User identities are stored as external IDs with "gerrit" as scheme. The user string obtained from Siteminder (e.g. the value in the "SM_USER" HTTP header) is stored as ID in the external ID.

Part of Gerrit Code Review