Authentication & Authorization
Implement robust authentication and authorization mechanisms for processes and users accessing your Erlang services.
Authentication & Authorization is a free Erlang OTP: Distributed & Fault-Tolerant Systems Programming lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Erlang OTP: Distributed & Fault-Tolerant Systems Programming learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
AuthN & AuthZ Explained
In distributed systems, knowing who is accessing your services and what they are allowed to do is critical for security. This is where authentication and authorization come in.
- Authentication (AuthN): Verifies the identity of a user or process. It answers the question, "Who are you?"
- Authorization (AuthZ): Determines if an authenticated user or process has permission to perform a specific action or access a resource. It answers, "What are you allowed to do?"
They work hand-in-hand to secure your Erlang applications.
Identifying Users
For user authentication, we typically verify credentials like a username and password. In Erlang, you might have a dedicated service (often a GenServer) responsible for managing user accounts and validating login attempts.
This service would receive a login request, check the provided credentials against stored data, and respond with either success or failure. On success, it might issue a session ID or token.
Building an Auth GenServer
Let's create a very basic auth_service using GenServer. For simplicity, it will store a hardcoded user and password. In a real system, you'd integrate with a database and securely hash passwords.
Our auth_service will have a login/2 function that clients can call to authenticate.
Runnable Auth Service
Try running this simple authentication service. You can call auth_service:login("user", "pass") and auth_service:login("wrong", "pass") to see the different responses.
-module(auth_service).
-behaviour(gen_server).
-export([start_link/0, login/2]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
% Client API
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
login(Username, Password) ->
gen_server:call(?MODULE, {login, Username, Password}).
% GenServer Callbacks
init([]) ->
% Store a simple user/pass for demonstration
Users = #{<<"user">> => <<"pass">>},
{ok, Users}.
handle_call({login, Username, Password}, _From, State) ->
case maps:get(Username, State, undefined) of
Password ->
{reply, {ok, <<"authenticated">>}, State};
_ ->
{reply, {error, <<"invalid_credentials">>}, State}
end;
handle_call(_Request, _From, State) ->
{reply, {error, unknown_request}, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.What Can You Do?
Once a user is authenticated, the next step is authorization. This means deciding what actions they are allowed to perform. A common way to manage this is through Role-Based Access Control (RBAC).
- Roles: Groups of permissions (e.g.,
admin,editor,viewer). - Permissions: Specific actions (e.g.,
create_post,edit_post,delete_post).
Users are assigned roles, and roles are assigned permissions.
Role-Based Access Control
We can extend our auth_service (or a separate service) to manage roles and permissions. It would need to know:
- Which roles a user has.
- Which permissions each role grants.
Then, when a service needs to check if a user can perform an action, it asks the authorization service.
Auth Service with RBAC
Here's an updated auth_service that includes a basic RBAC mechanism. It defines roles and permissions and allows checking if a user has a specific permission.
Try calling auth_service:check_permission("user", "read_data") and auth_service:check_permission("user", "delete_data") after logging in.
-module(auth_service).
-behaviour(gen_server).
-export([start_link/0, login/2, check_permission/2]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
% Client API
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
login(Username, Password) ->
gen_server:call(?MODULE, {login, Username, Password}).
check_permission(Username, Permission) ->
gen_server:call(?MODULE, {check_permission, Username, Permission}).
% GenServer Callbacks
init([]) ->
Users = #{
<<"user">> => #{
password => <<"pass">>,
roles => [<<"viewer">>, <<"editor">>]
},
<<"admin">> => #{
password => <<"admin_pass">>,
roles => [<<"admin">>, <<"viewer">>]
}
},
Roles = #{
<<"viewer">> => [<<"read_data">>],
<<"editor">> => [<<"read_data">>, <<"write_data">>],
<<"admin">> => [<<"read_data">>, <<"write_data">>, <<"delete_data">>]
},
{ok, #{users => Users, roles => Roles}}.
handle_call({login, Username, Password}, _From, State) ->
Users = maps:get(users, State),
case maps:get(Username, Users, undefined) of
#{password := Password} ->
{reply, {ok, <<"authenticated">>}, State};
_ ->
{reply, {error, <<"invalid_credentials">>}, State}
end;
handle_call({check_permission, Username, Permission}, _From, State) ->
Users = maps:get(users, State),
Roles = maps:get(roles, State),
case maps:get(Username, Users, undefined) of
#{roles := UserRoles} ->
HasPermission = lists:any(
fun(Role) ->
case maps:get(Role, Roles, []) of
RolePermissions when is_list(RolePermissions) ->
lists:member(Permission, RolePermissions);
_ -> false
end
end,
UserRoles
),
{reply, HasPermission, State};
_ ->
{reply, false, State} % User not found or not authenticated
end;
handle_call(_Request, _From, State) ->
{reply, {error, unknown_request}, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.Securing Your Services
Once you have an authentication and authorization service, other services in your system can use it. A typical flow looks like this:
- Client Authenticates: Calls
auth_service:login/2. - Receives Session/Token: If successful, the client gets a session ID or token (e.g., a process ID, or a more complex JWT).
- Client Makes Authorized Request: When calling another service (e.g.,
data_service), the client includes its session/token and the action it wants to perform. - Service Authorizes: The
data_servicecallsauth_service:check_permission/2using the client's identity and the requested action. - Service Responds: If authorized, the action proceeds; otherwise, an error is returned.
Beyond Basic Auth
While our examples are simple, real-world systems need more:
- Password Hashing: Never store plaintext passwords. Use strong hashing algorithms like
bcryptorpbkdf2. - Session Management: Securely generate, store, and validate session tokens. Ensure they expire and can be revoked.
- Auditing: Log all authentication attempts and authorization checks for security monitoring and forensics.
- External Identity Providers: Integrate with OAuth2/OpenID Connect for single sign-on.
Erlang's concurrency makes it great for building robust auth services.
AuthN vs AuthZ Check
Consider a user trying to access a secure document in an Erlang application.
Recap: Securing Services
We've covered the fundamentals of authentication and authorization in Erlang:
- Authentication (AuthN) verifies identity ("Who are you?").
- Authorization (AuthZ) determines permissions ("What can you do?").
- We built a simple
auth_serviceusing GenServer for both user login and role-based access control (RBAC). - Understanding how to integrate these services is key to building secure and robust distributed Erlang applications.
Next, explore how to protect sensitive data itself within your Erlang applications.
Frequently asked questions
Is the “Authentication & Authorization” lesson free?
Yes — the full text of “Authentication & Authorization” is free to read here on the web, and the Erlang OTP: Distributed & Fault-Tolerant Systems Programming course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Erlang OTP: Distributed & Fault-Tolerant Systems Programming course, upgrade to CoddyKit PRO.
What will I learn in “Authentication & Authorization”?
Implement robust authentication and authorization mechanisms for processes and users accessing your Erlang services. You practise Erlang OTP: Distributed & Fault-Tolerant Systems Programming with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Erlang OTP: Distributed & Fault-Tolerant Systems Programming?
No prior experience is required. Erlang OTP: Distributed & Fault-Tolerant Systems Programming on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Authentication & Authorization” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Erlang OTP: Distributed & Fault-Tolerant Systems Programming lesson?
Yes. Every Erlang OTP: Distributed & Fault-Tolerant Systems Programming lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Secure Node Communication (TLS)
- Authentication & Authorization
- Protecting Sensitive Data
- Hardening the Distribution Cookie & Node Access