2. Setup User Mapping

Every authenticated HTTP request sent to the OnDemand portal has a REMOTE_USER. This REMOTE_USER can be an email like annie.oakley@osc.edu and needs to be mapped to a Linux system user like aoakley.

This is what we call user mapping. Mapping apache’s REMOTE_USER from an authenticated request to a Linux system user.

Mapping to the local system user not only restricts access of OnDemand to local users but it is also required by the OnDemand proxy to traffic the HTTP data to the user’s corresponding per-user NGINX (PUN) server.

Versions prior to 2.0 relied on user_map_cmd to do this. Since 2.0 you should use the simpler and faster user_map_match.

Both with variations will be discussed here.

2.1. Remote User

It’s worth discussusing where REMOTE_USER is comfing from. When apache has successfully authenticates a request it sets the variable REMOTE_USER from, well, the remote.

This is generally a return value from the authentication system like an open id connect provider. It’s common for this to be an email address.

You can configure user_env to use something other than REMOTE_USER, but it’s unlikely you should need to.

If you’re using an OpenID Connect provider you may need to set oidc_remote_user_claim as this setting tells apache how to set REMOTE_USER from the claim response.

2.2. Reguluar Expression User Mapping

The simplest and fastest way to map a REMOTE_USER to a system user is through user_map_match. It isn’t directly regular expression matching, but it’s close enough for most use cases. See it’s documentation for examples and more.

2.3. Dex Automatic Configuration

When using the OpenId Connector dex and setting oidc_remote_user_claim to email we automatically set user_map_match to ^([^@]+)@.*$ as a convienience.

2.4. User Map Command for Advanced Mappings

Versions prior to 2.0 provided a default user_map_cmd in /opt/ood/ood_auth_map/bin/ood_auth_map.regex. We no longer distribute this file.

Sites instead need to write their own mapping script should they need this capability. Set this custom mapping script in the user_map_cmd configuration and be sure to make this mapping script executable.


Be aware, this script is executed on every request.

Let’s take a simple example. It uses bash’s builtin regular expression matching against ([^@]+)@osc.edu - an osc dot edu email address. If that matches against $1 (the REMOTE_USER) after it’s url-decoded, then we return an all lowercase version of the first part of an email address.

The contract this script has with ood is that REMOTE_USER is url-encoded and passed into it as the first arguement, $1.

The script will return 0 and output the match if it can correctly map the user. Otherwise, if it fails, it will output nothing and exit 1.


function urldecode() { : "${*//+/ }"; echo -e "${_//%/\\x}"; }

INPUT_USER=$(urldecode $1)

if [[ $INPUT_USER =~ $REX ]]; then
  echo "$MATCH" | tr '[:upper:]' '[:lower:]'
  # can't write to standard out or error, so let's use syslog
  logger -t 'ood-mapping' "cannot map $INPUT_USER"

  # and exit 1
  exit 1

If I were to run and test this script - it would return values like these:

$ /opt/site/custom_mapping.sh 'Annie.Oakley%40osc.edu'
$ /opt/site/custom_mapping.sh 'jessie%40osc.edu'
$ /opt/site/custom_mapping.sh 'jessie.owens%40harvard.edu'
$ echo $?
$ 1
$ journalctl -t ood-mapping
-- Journal begins at Tue 2020-06-02 06:45:03 EDT, ends at Wed 2022-01-19 15:11:37 EST. --
Jan 19 15:03:14 localhost.localdomain ood-mapping[149352]: cannot map jessie.owens@harvard.edu

2.5. File User Mapping

This script parses a mapfile with each entry given in the following format:

"authenticated_username" local_username

and separated by newlines. The script will systematically parse each line in the mapfile looking for a match to the authenticated_username. When a match is found it breaks from the scan and outputs the local_username to STDOUT.


Be aware, this script is executed and reads a user mapping file on every request.

/opt/ood/ood_auth_map/bin/ood_auth_map.mapfile [OPTIONS] <REMOTE_USER>

The options for this script are:

-f <file>, --file <file>

Default: /etc/grid-security/grid-mapfile

File used to scan for matches.

2.5.1. Examples for the MapFile script

To scan the default grid-mapfile using a URL-encoded authenticated username:

$ /opt/ood/ood_auth_map/bin/ood_auth_map.mapfile 'http%3A%2F%2Fcilogon.org%2FserverA%2Fusers%2F58606%40cilogon.org'

To scan a custom mapfile using an authenticated username:

$ /opt/ood/ood_auth_map/bin/ood_auth_map.mapfile --file '/path/to/mapfile' 'opaque_remote_username'

If no match is found within the mapfile for the supplied authenticated username that an empty string is returned instead:

$ /opt/ood/ood_auth_map/bin/ood_auth_map.mapfile 'this_remote_username_does_not_exist'


2.6. Debugging User Mapping

When debugging user mapping, it’s always helpful to increase the lua_log_level to debug.

In doing so you’ll see messages like that detail the mapping input, output and times like Mapped 'jeff@localhost' => 'jeff' [0.089 ms].

The full message would look like this.

/var/log/httpd/error.log:[Wed Jan 19 20:45:36.955855 2022] [lua:debug] [pid 39:tid 140070995539712] @/opt/ood/mod_ood_proxy/lib/ood/user_map.lua(21): [client] Mapped 'jeff@localhost' => 'jeff' [0.089 ms], referer: http://localhost:5556/