11. Applications and Machines or Services¶

eduMFA supports authentication schemes, that happen on other machines or services with special applications.

eduMFA lets you define Machine Resolvers to connect to existing machine stores. The idea is for users to be able to authenticate on those client machines. Not in all cases an online authentication request is possible, so that authentication items can be passed to those client machines.

In addition you need to define, which application or service on the client machine the user should authenticate to. Different application require different authentication items.

Therefore eduMFA can define application types. At the moment eduMFA knows the application luks, offline and ssh. You can write your own application class, which is defined in Application Class.

You need to attach a token via an application to a client machine or service. Each application type can work with certain token types and each application type can use additional parameters.

Note

Not all tokentypes work well with all applications!

11.1. SSH¶

Currently working token types: SSH

Parameters:

user (optional, default=root)

service_id (required)

When the SSH token type is assigned to a client, the user specified in the user parameter can login with the private key of the SSH token.

The service_id identifies the SSH servers or group of SSH servers, where the login is allowed to occur. Read more about Service IDs.

11.1.1. authorized keys command¶

To facilitate this, the SSH server fetches the managed SSH keys from the eduMFA server on demand. The SSH server uses the AuthorizedKeysCommand in the sshd_config to do this.

There is an Python script edumfa-authorizedkey in the eduMFAadm repository. Note, that this script currently does not support the service_id. The tools/ directory of the eduMFA Server ships a shell script edumfa-authorizedkeys that supports the service_id.

In the sshd_config file you need to configure the AuthorizedKeysCommand accordingly. Set it to e.g.:

edumfa-authorizedkeys

This will fetch the SSH public keys for the requesting machine and the given user.

If you are using the shell script you need to configure the eduMFA Server and the service account at the top of the script.

The Python script however expects a configuration file /etc/edumfa/authorizedkeyscommand which looks like this:

[Default]
url=https://localhost
admin=admin
password=test
nosslcheck=False
service_id=webservers

In this example the SSH keys that are attached to the service_id “webservers” are fetched from the eduMFA server.

11.1.2. managing in WebUI¶

The administrator can view all SSH keys attached to service in the WebUI at Tokens -> Token Applications. There the administrator can filter for service_ids., to find all SSH keys that are attached e.g. to webservers.

Note

To disable a SSH key for all servers, you simply can disable the distinct SSH token in eduMFA.

Warning

In a productive environment you should not set nosslcheck to true, otherwise you are vulnerable to man in the middle attacks.

11.2. LUKS¶

Currently working token types: Yubikey Challenge Response

Parameters:

slot The slot to which the authentication information should be written

partition The encrypted partition (usually /dev/sda3 or /dev/sda5)

These authentication items need to be pulled on the client machine from the eduMFA server.

Thus, the following script need to be executed with root rights (able to write to LUKS) on the client machine:

eduMFA-luks-assign @secrets.txt --clearslot --name salt-minion

For more information please see the man page of this tool.

11.3. Offline¶

Currently working token types: HOTP.

Parameters:

user The local user, who should authenticate. (Only needed when calling machine/get_auth_items)

count The number of OTP values passed to the client.

The offline application also triggers when the client calls a /validate/check. If the user authenticates successfully with the correct token (serial number) and this very token is attached to the machine with an offline application the response to validate/check is enriched with a “auth_items” tree containing the salted SHA512 hashes of the next OTP values.

The client can cache these values to enable offline authentication. The caching is implemented in the eduMFA PAM module.

The server increases the counter to the last offline cached OTP value, so that it will not be possible to authenticate with those OTP values available offline on the client side.

11.3.1. managing in WebUI¶

The administrator can view all offline tokens in the WebUI at Tokens -> Token Applications.