Lua Support

Nauthilus has Lua 5.1 support in all areas of the service. To understand the interfaces, you must first get an idea of what happens with an incoming authentication request.

Authentication workflow

An incoming authentication request first enters the brute_force check. After that it continues with the environment stage. After that has passed, it continues to process the request in a password backend. When the final result for the request was obtained, it passes subject sources.

Subject sources may change the backend result in one or the other way (accepting a formerly rejected message or vice versa). This is especially useful for other remote services that can influence the authentication process.

After all this has finished, it is possible to do some post actions, which are run independent of all other steps in the whole pipeline and therefore can not influence the final result anymore.

Policy-aware action semantics

Nauthilus distinguishes synchronous Lua actions from Lua POST-Actions.

Synchronous Lua actions are configured with action types such as brute_force, lua, tls_encryption, relay_domains, and rbl. In policy-authoritative paths, the selected policy decision dispatches them through the registered obligation auth.obligation.lua_action.dispatch and Nauthilus waits for the action before the request continues.

The triggering check, environment control, or environment source only emits facts. The action runs only when the selected decision includes the dispatch obligation. This keeps reports, observe-mode comparisons, and mutable side effects aligned with the same policy decision.

Lua POST-Actions use the post action type. They run after the request-time decision context is known and must not change the final decision, response marker, response message, or FSM terminal state. In auth.policy authoritative paths, POST-Action enqueueing is requested through the registered obligation auth.obligation.lua_post_action.enqueue. Brute-force counter and learning updates are requested through auth.obligation.brute_force.update.

Observe-mode policy evaluation reports planned custom obligations but never executes them, so it does not dispatch synchronous Lua actions, enqueue custom POST-Actions, or mutate brute-force state.

In the following sequence diagram you can see the processing of the request in more detail.

Additional things to know

When starting the server, it is possible to call an init script, which may be used to register prometheus elements, start connection tracker or define custom redis pools. The latter is interesting, if you prefer using other redis servers for all your custom Lua scripts.

While runtime...

When an incoming authentication request is started, a Lua context is created.

All parts of a request share that common request context. Lua scripts can set arbitrary data in the context and read/delete things from there.

Lua scripts can modify the final log line by adding key-value pairs from each script.

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Configuration

For the configuration, please have a look at the configuration file document.

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Lua components

Each component does provide a set of global functions, constants, ... and requires a well-defined response from each request.

Every Lua script that has been configured is pre-compiled and kept in memory for future use. To make script changes, you must reload the service.

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Lua libraries

Nauthilus does automatically preload Lua modules.

This is the list of modules that are currently available:

Loader name	Description
nauthilus_mail	E-Mail functions
nauthilus_password	Password compare and validation functions
nauthilus_redis	Redis related functions
nauthilus_misc	Country code and sleep functions
nauthilus_context	Global Lua context accross all States in Nauthilus
nauthilus_ldap	LDAP related functions
nauthilus_backend	Backend related functions
nauthilus_http_request	HTTP request header functions
nauthilus_http_response	HTTP response functions (headers, status, body; environment/subject sources MUST NOT send a body)
nauthilus_policy	Request-local policy attribute emission
nauthilus_i18n	Policy localization helpers and startup catalog overlays
nauthilus_cbor	CBOR encode/decode helpers
nauthilus_prometheus	Prometheus metrics functions
nauthilus_soft_whitelist	Soft whitelist functions
nauthilus_brute_force	Brute force prevention functions
nauthilus_dns	DNS related functions
nauthilus_cache	In-process cache functions
nauthilus_psnet	Network connection manager functions
nauthilus_opentelemetry	OpenTelemetry tracing functions
nauthilus_util	Common utility functions
glua_crypto	gluacrpyto project on Github
glua_http	gluahttp project on Github

In addition to these Nauthilus-specific modules, the gopher-lua-libs collection is automatically preloaded, providing access to modules like json, yaml, time, db, tcp, and more.

Example:

local nauthilus_redis = require("nauthilus_redis")

local nauthilus_builtin_context = require("nauthilus_context")

-- Gopher-Lua-Libs

local crypto = require("crypto")

local db = require("db")

local time = require("time")

-- Glua-Crypto

local crypto = require("glua_crypto") -- provides sha1 and others...

Actions

Whenever a brute froce attack is recognized, actions may be called. The request will wait until all requests have finished. Actions are processed by a central action worker. No results are returned to the regular request, so actions in general do their own logging!

Lua actions run only when the selected policy decision dispatches the corresponding obligation. Synchronous actions wait for the worker to finish.

Environment Sources

Lua environment sources run in the pre-auth phase alongside built-in checks such as geoip, rbl, tls_encryption and relay_domains. They are useful when the environment context itself should decide whether the request may continue. Lua environment sources are executed in parallel starting with v1.8.9. As soon as any environment source has triggered, the request will reject the authentication process after all environment sources have finished, and the results are aggregated.

Version change in 1.8.9

Since version 1.8.9, Lua environment and subject sources are executed in parallel. Nauthilus waits for all scripts to finish and then aggregates their results:

• Environment sources: triggered=true if any script reports ENVIRONMENT_TRIGGER_YES; abort flag is set if any script requests ENVIRONMENT_ABORT_YES; the first error aborts the whole operation; the first status_message set is used.
• Subject sources: an action is taken if any subject source requests it; backend_result attributes from multiple subject sources are merged (later keys overwrite earlier ones); remove-attributes are unioned; the first error aborts; the first status_message set is used. Each script runs with its own Lua state and per-script timeout. Do not rely on execution order between scripts.

Lua environment sources can return an abort flag to skip remaining built-in pre-auth checks.

Lua backend

The Lua backend can be used for password checks and request modes such as no-auth, list-accounts, and TOTP-aware flows.

The backend can accept a request or reject it. It has full access to all meta information that are delivered from the incoming request.

Subject Sources

There may exist remote services that may be contacted after the main backend authentication proccess returned its first
result. Think of something like GeoIP service or some IP white/blacklisting. Even a request that might have authenticated correctly may be rejected to a policy violation from such a service. Therefor subject sources have the power to overwrite the result from a backend.

You can also use subject sources to retrieve additional information from databases or LDAP and add additional attributes to the remaining result. This is useful for setups, where Nauthilus may also take the role of a Dovecot proxy. Users may get routed to different mail stores upon successful authentication. For this, you may retrieve the current backend server list with servers that have been checked as being alive by backend health checks and select one for the current client request.

info

Subject sources never affect caching! This is important, because otherwise valid credentials might result in storing them in the negative password cache or vice versa for invalid credentials.

warning

You always have to deal with the "request.authenticated" flag! If you don't care enough, you might acidentially reject legitimate authenticated users or allow bad guys.

Post actions

Post actions are actions, which run after the request hast come to its final result. Its main purpose is to start some automated things like doing statistics stuff, sending messages to operators or anything else that does not require fast instant processing.

As an example have a look at the telegram script. Lua scripts in earlier stages of the process may provide some information by using the Lua context. The telegram script may pick up these information and decide to send out some notifications to an operator channel.

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Required functions and constants

Every Lua script must provide a pre-defined Lua function with a request parameter. Concerning the actual script, there is a requried return statement.

Nauthilus will look for these functions and parses the results.

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Common request fields for all Lua scripts

The following request fields are supported

Name	Type	Precense	Additional info
debug	bool	always	-
repeating	bool	maybe	-
user_found	bool	maybe	-
authenticated	bool	maybe	-
no_auth	bool	always	true, if the reuqest is used to retrieve user information
service	string	always	Nauthilus endpoint like "dovecot" or "nginx"
session	string	always	-
client_ip	string	always	-
client_port	string	always	-
client_host	string	maybe	-
client_net	string	maybe	Available in conjunction with brute-force-actions
client_id	string	maybe	-
user_agent	string	maybe	-
local_ip	string	always	-
local_port	string	always	-
username	string	always	-
account	string	maybe	Subject and post actions
unique_user_id	string	maybe	Used with OIDC subject
display_name	string	maybe	-
password	string	always	-
protocol	string	always	-
brute_force_bucket	string	maybe	Available in conjunction with brute-force-actions
environment	string	maybe	In actions, if an environment source or control has triggered
status_message	string	always	Current status message returned to client, if auth request failed
ssl	string	maybe	HAproxy: %[ssl_fc]
ssl_session_id	string	maybe	HAproxy: %[ssl_fc_session_id,hex]
ssl_client_verify	string	maybe	HAproxy: %[ssl_c_verify]
ssl_client_dn	string	maybe	HAproxy: %{+Q}[ssl_c_s_dn]
ssl_client_cn	string	maybe	HAproxy: %{+Q}[ssl_c_s_dn(cn)]
ssl_issuer	string	maybe	HAproxy: %{+Q}[ssl_c_i_dn]
ssl_client_not_before	string	maybe	HAproxy: %{+Q}[ssl_c_notbefore]
ssl_client_not_after	string	maybe	HAproxy: %{+Q}[ssl_c_notafter]
ssl_subject_dn	string	maybe	HAproxy: %{+Q}[ssl_c_s_dn]
ssl_issuer_dn	string	maybe	HAproxy: %{+Q}[ssl_c_i_dn]
ssl_client_subject_dn	string	maybe	HAproxy: %{+Q}[ssl_c_s_dn]
ssl_client_issuer_dn	string	maybe	HAproxy: %{+Q}[ssl_c_i_dn]
ssl_protocol	string	maybe	HAproxy: %[ssl_fc_protocol]
ssl_cipher	string	maybe	HAproxy: %[ssl_fc_cipher]
ssl_serial	string	maybe	SSL certificate serial number
ssl_fingerprint	string	maybe	SSL certificate fingerprint
brute_force_counter	number	always	Current brute force attempt counter
account_field	string	maybe	The name of the field that contains the account
method	string	maybe	HTTP method (e.g., "GET", "POST")
oidc_cid	string	maybe	OIDC Client ID
saml_entity_id	string	maybe	SAML Service Provider Entity ID
grant_type	string	maybe	OIDC grant/flow type (e.g. authorization_code, device_code)
oidc_client_name	string	maybe	Human-readable OIDC client name
redirect_uri	string	maybe	OIDC redirect URI from current flow
mfa_completed	bool	maybe	Whether MFA was completed in current flow
mfa_method	string	maybe	MFA method used (totp, webauthn, recovery)
requested_scopes	table	maybe	Requested OIDC scopes as Lua table
user_groups	table	maybe	User group memberships (for example LDAP memberOf)
allowed_client_scopes	table	maybe	Scopes configured on current OIDC client
allowed_client_grant_types	table	maybe	Grant types configured on current OIDC client
log_format	string	always	Configured log format ("default" or "json")
log_level	string	always	Configured log level
logging	table	always	Table containing log_format and log_level
latency	number	always	Request processing latency
http_status	number	always	HTTP status code returned to the client
redis_prefix	string	always	Configured Redis key prefix

note

TLS-related values may be retrieved from Nginx and as a fallback tried to be retrieved from HAproxy headers.

tip

It is always a good idea to check the value of a request field, before using it.

Environment Sources

A Lua environment source script must provide the following function:

---@param request table
---@return boolean, boolean, number
function nauthilus_call_environment(request)
  return triggered, abort, result -- See details below
end

important

It must return three values: the trigger state, an abort flag for remaining pre-auth checks, and the script result status.

Constants for the returned result

Constant	Meaning	Value	Category
nauthilus_builtin.ENVIRONMENT_TRIGGER_NO	The environment source has not been triggered	false	trigger
nauthilus_builtin.ENVIRONMENT_TRIGGER_YES	The environment source has been triggered and the request must be rejected	true	trigger
nauthilus_builtin.ENVIRONMENT_ABORT_NO	Process other environment controls and sources	false	skip_flag
nauthilus_builtin.ENVIRONMENT_ABORT_YES	After finishing the script, skip all other environment controls and sources	true	skip_flag
nauthilus_builtin.ENVIRONMENT_RESULT_OK	The script finished without errors	0	failure_info
nauthilus_builtin.ENVIRONMENT_RESULT_FAIL	Something went wrong while executing the script	1	failure_info

Request fields

Only common request fields are present.

Subject Sources

A Lua subject source script must provide the following function:

---@param request table
---@return boolean, number
function nauthilus_call_subject(request)
  if request.authenticated then
    -- do something
  end

  return subject_action, result -- See details below
end

important

It must return two values: the subject action and the script result status.

Constants for the returned result

Constant	Meaning	Value	Category
nauthilus_builtin.SUBJECT_ACCEPT	The request must be accepted	false	subject_action
nauthilus_builtin.SUBJECT_REJECT	The request has to be rejected	true	subject_action
nauthilus_builtin.SUBJECT_RESULT_OK	The script finished without errors	0	subject_info
nauthilus_builtin.SUBJECT_RESULT_FAIL	Something went wrong while executing the script	1	subject_info

Request fields

Only common request fields are present.

Actions (including post)

A Lua action script must provide the following function:

---@param request table
---@return number
function nauthilus_call_action(request)
  if request.no_auth then
    -- Example post action: Store request information in database
  end

  return failure_info -- See details below
end

important

Actions must return the script status constant.

Constants for the returned result

Constant	Meaning	Value	Category
nauthilus_builtin.ACTION_RESULT_OK	The script finished without errors	0	failure_info
nauthilus_builtin.ACTION_RESULT_FAIL	The script finished with errors	1	failure_info

Request fields

Only common request fields are available.

Lua Backend

The Lua backend script must provide the following function:

---@param request table
---@return number, userdata
function nauthilus_backend_verify_password(request)
  local backend_result_object = backend_result:new()
  -- Do something with backend_result_object

  return failure_info, backend_result_object -- See details below
end

For user account listing, the following function is required:

---@param request table
------@return number, table
function nauthilus_backend_list_accounts(request)
  local accounts = {}

  return failure_info, accounts -- See details below
end

If you plan on adding TOTP-keys for your users, you must provide the follwing function:

---@param request table
---@return number
function nauthilus_backend_add_totp(request)
  return failure_info -- See details below
end

important

The backend must return the result status constant and a backend result object

Constants for the returned result

Constant	Meaning	Value	Category
nauthilus_builtin.BACKEND_RESULT_OK	The script finished without errors	0	failure_info
nauthilus_builtin.BACKEND_RESULT_FAIL	The script finished with errors	1	failure_info

Request fields

Function nauthilus_backend_verify_password request fields

Only common request fields are used.

Function nauthilus_backend_list_accounts request fields

Only "debug" and "session" from the common requests are available.

Function nauthilus_backend_add_totp request fields

Only "debug" and "session" from the common requests as well as "totp_secret" (string) are available.

Cache flush callback

If auth.backends.lua.backend.default.cache_flush_script_path is configured, Nauthilus executes a dedicated Lua callback during:

• DELETE /api/v1/cache/flush
• DELETE /api/v1/cache/flush/async

The script must provide:

---@param request table
---@return table|nil, string|nil
function nauthilus_cache_flush(request)
  local additional_keys = {
    request.redis_prefix .. ":custom:" .. request.username
  }

  local account_name = "account-value"

  return additional_keys, account_name
end

Return contract:

• First return value: table (array) with additional Redis keys to delete. Non-string items are ignored.
• Second return value: optional account name (string). If non-empty, Nauthilus skips account lookup and uses this value.

Request fields

Common request fields are available. For cache flush calls, the following are guaranteed to be set:

• request.username: user name from the flush request payload
• request.session: generated request GUID
• request.redis_prefix: configured Redis prefix (storage.redis.prefix)

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UserData object backend_result

The nauthilus_backend_result object can be initialized in the Lua backend and in Lua subject sources. The following methods exist:

backend

Name	Meaning
authenticated	Set or get the authentication status
user_found	Set or get the user found flag which indicated, if the backend found the user
account_field	Set or get the account field name, which must have been added to a list of result attributes
totp_secret_field	Set or get the TOTP secret field name, which must have been added to the result attributes
totp_recovery_field	Not yet implemented
unique_user_id_field	Set or get the unique user id field, which must have been added to the result attributes
display_name_field	Set or get the display name field, which must have been added to the result attributes
attributes	Set or get the result attributes as a Lua table

subject sources

Subject sources only have an "attributes" method. While Lua backends do return a nauthlus_backend_result directly, subject sources can only apply it with a Lua function called "nauthilus_backend.apply_backend_result(backend_result_object)".

Attributes can not overwrite existing attributes!

Example usage for nauthilus_backend_result

local attributes = {}
attributes["account"] = "bob"

local b = nauthilus_backend_result.new()
b:attributes(attributes) -- Add the table
b:account_field("account") -- Attributes contain a key "account" for the account field
b:authenticated(true) -- User is authenticated
b:user_found(true) -- The user was found

Endpoints /api/v1/mail/dovecot, /api/v1/generic/user and /api/v1/generic/json

"attributes" represent a common result store for a backend query. All fields that have been set by *_field methods will be used for further internal processing, while all other attributes will be converted to HTTP-response-headers, which will be sent back to the client application that talked to Nauthilus. These headeres will be prefixed with X-Nauthilus-.

For the generic endpoints, "attributes" will bew returned in the JSON respone.

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Additional notes

Nauthilus uses the gopher-lua-libs library in all Lua scripts. Please have a look at their documentation for all the modules that can directly be used in Nauthilus scripts:

gopher-lua-libs on Github