Introduction

This document describes the API provided by the VPN portal. The API can be used by applications wanting to integrate with the VPN software to make it easy for users to configure their VPN.

The API is pragmatic "REST", keeping things as simple as possible without obsessing about the proper HTTP verb. There are no PUT and DELETE requests, just simple GET and POST requests that use "form submit". The responses are always application/json though.

Standards

OAuth 2.0 is used to provide the API. The following documents are relevant for implementations and should be followed to the letter except when stated differently:

The OAuth 2.0 Authorization Framework;
The OAuth 2.0 Authorization Framework: Bearer Token Usage;
OAuth 2.0 for Native Apps (use latest version of specification);
Proof Key for Code Exchange by OAuth Public Clients

Implementing OAuth 2.0 correctly is not easy, there are a number of sample applications available for various platforms that can (and probably should) be used as a basis:

Definitions

A VPN service running at a particular domain is called an instance, e.g. demo.eduvpn.nl. An instance can have multiple profiles, e.g. internet and office.

Instance Discovery

For an application to discover which instances are available to show to the user a JSON document can be retrieved. For example eduVPN has a document available at https://static.eduvpn.nl/instances.json.

The document looks like this:

{
    "instances": [
        {
            "base_uri": "https:\/\/surf.eduvpn.nl\/",
            "display_name": "SURF",
            "logo_uri": "https:\/\/static.eduvpn.nl\/img\/surfnet.png"
        },
     
        ...

    ],
    "seq": 25,
    "signed_at": "2017-05-11 14:55:03",
    "version": 1
}

The base_uri can be used to perform the API Discovery, see below. The other fields can be used to enhance the UI for users using the application by providing a logo and a human readable name for the instance. Users also SHOULD have the option to provide their own base_uri in the application UI if their favorite provider is not listed.

Validation

When downloading the instance discovery file, you also MUST fetch the signature file, which is located in the same folder, but has the .sig extension, e.g. https://static.eduvpn.nl/instances.json.sig.

Using libsodium you can verify the signature using the public key(s) that you hard code in your application. The signature file contains the Base64-encoded signature. See this document for various language bindings.

The flow:

Download instances.json;
Download instances.json.sig;
Verify the signature using libsodium and the public key stored in your application
If you already have a cached version, verify the seq field of the new file is higher than the seq in the cached copy (see Caching section);
Overwrite the cached version if appropriate.

API Discovery

The OAuth and API endpoints can be discovered by requesting a JSON document from the instance, based on the base_uri from the "Instance Discovery" above. This is the content of https://demo.eduvpn.nl/info.json:

{
    "api": {
        "http://eduvpn.org/api#1": {
            "authorization_endpoint": "https://demo.eduvpn.nl/portal/_oauth/authorize",
            "create_config": "https://demo.eduvpn.nl/portal/api.php/create_config",
            "profile_list": "https://demo.eduvpn.nl/portal/api.php/profile_list",
            "system_messages": "https://demo.eduvpn.nl/portal/api.php/system_messages",
            "user_messages": "https://demo.eduvpn.nl/portal/api.php/user_messages"
        },
        "http://eduvpn.org/api#2": {
            "api_base_uri": "https://demo.eduvpn.nl/portal/api.php",
            "authorization_endpoint": "https://demo.eduvpn.nl/portal/_oauth/authorize",
            "token_endpoint": "https://demo.eduvpn.nl/portal/oauth.php/token"
        }
    }
}

NOTE: new implementations MUST use http://eduvpn.org/api#2!

Authorization Request

The authorization_endpoint is then used to obtain an access token by providing it with the following query parameters, they are all required, despite some of them being OPTIONAL according to the OAuth specification:

client_id: the ID that was registered, see below;
redirect_uri; the URL that was registered, see below;
response_type: always code;
scope: this is always config;
state: a cryptographically secure random string, to avoid CSRF;
code_challenge_method: always S256;
code_challenge: the code challenge (see RFC 7636).

The authorization_endpoint URL together with the query parameters is then opened using a browser, and eventually redirected to the redirect_uri where the application can extract the access_token field from the URL fragment. The state parameter is also added to the fragment of the redirect_uri and MUST be the same as the state parameter value of the initial request. The response also includes expires_in that indicates when the access token will expire.

Using the API

Using the access_token some additional server information can be obtained, as well as configurations created. The examples below will use cURL to show how to use the API.

If the API responds with a 401 it may mean that the user revoked the application's permission. Permission to use the API needs to be requested again in that case. The URLs MUST be taken from the info.json document described above.

Profile List

This call will show the available VPN profiles for this instance. This will allow the application to show the user which profiles are available and some basic information, e.g. whether or not two-factor authentication is enabled.

$ curl -H "Authorization: Bearer abcdefgh" \
    https://demo.eduvpn.nl/portal/api.php/profile_list

The response looks like this:

{
    "profile_list": {
        "data": [
            {
                "display_name": "Internet Access",
                "profile_id": "internet",
                "two_factor": false
            }
        ],
        "ok": true
    }
}

User Info

API VERSION 2 ONLY

This call will show information about the user, whether or not the user is enrolled for 2FA and whether or not the user is prevented from connecting to the VPN.

$ curl -H "Authorization: Bearer abcdefgh" \
    https://demo.eduvpn.nl/portal/api.php/user_info

The response looks like this:

{
    "user_info": {
        "data": [
            {
                "two_factor_enrolled": false,
                "is_disabled": false
            }
        ],
        "ok": true
    }
}

Create a Configuration

A call that can be used to get a full working OpenVPN configuration file including certificate and key. This MUST NOT be used by "Native Apps". Instead the separate /create_keypair and /profile_config MUST be used as they allow for obtaining a new configuration without generating a new certificate/key.

$ curl -H "Authorization: Bearer abcdefgh" \
    -d "display_name=eduVPN%20for%20Android&profile_id=internet" \
    https://demo.eduvpn.nl/portal/api.php/create_config

This will send a HTTP POST to the API endpoint, /create_config with the parameters display_name and profile_id to indicate for which profile a configuration is downloaded.

The acceptable values for profile_id can be discovered using the /profile_list call as shown above.

The response will be an OpenVPN configuration file that can be used "as-is".

Create a Key Pair

API VERSION 2 ONLY

$ curl -H "Authorization: Bearer abcdefgh" \
    -d "display_name=eduVPN%20for%20Android" \
    https://demo.eduvpn.nl/portal/api.php/create_keypair

This will send a HTTP POST to the API endpoint, /create_keypair with the parameter display_name. It will only create a public and private key and return them.

{
    "create_keypair": {
        "data": {
            "certificate": "-----BEGIN CERTIFICATE----- ... -----END CERTIFICATE-----",
            "private_key": "-----BEGIN PRIVATE KEY----- ... -----END PRIVATE KEY-----"
        },
        "ok": true
    }
}

The certificate and the private key need to be combined with a profile configuration as <cert>...</cert> and <key>...</key> that can be obtained through the /profile_config call.

NOTE: a certificate is valid for ALL profiles of a particular instance, so if an instance has e.g. the profiles internet and office, only one certificate is required!

Profile Config

API VERSION 2 ONLY

Only get the profile configuration without certificate and private key.

$ curl -H "Authorization: Bearer abcdefgh" \
    "https://demo.eduvpn.nl/portal/api.php/profile_config?profile_id=internet"

The response will be an OpenVPN configuration file without the <cert> and <key> fields.

System Messages

$ curl -H "Authorization: Bearer abcdefgh" \
    https://demo.eduvpn.nl/portal/api.php/system_messages

The application is able to access the system_messages endpoint to see if there are any notifications available. These are the types of messages:

notification: a plain text message in the message field;
motd: a plain text "message of the day" (MotD) of the service, to be displayed to users on login or when establishing a connection to the VPN;
maintenance: an (optional) plain text message in the message field and a begin and end field with the time stamp;

All message types have the date_time field indicating the date the message was created. This can be used as a unique identifier.

The date_time, begin and end fields are in ISO 8601 format. Note that seconds are also included.

An example:

{
    "system_messages": {
        "data": [
            {
                "message": "Hello World!",
                "date_time": "2016-12-02T10:42:08Z",
                "type": "notification"
            }
        ],
        "ok": true
    }
}

The messages of type maintenance will be available through the API until they are no longer relevant. Messages of type notification will be always available through the API until an administrator (manually) removes it.

User Messages

$ curl -H "Authorization: Bearer abcdefgh" \
    https://demo.eduvpn.nl/portal/api.php/user_messages

These are messages specific to the user. It can contain a message about the user being blocked, or other personal messages from the VPN administrator.

These are the types of messages:

notification: a plain text message in the message field;

An example:

{
    "user_messages": {
        "data": [
            {
                "message": "Your account has been disabled. Please contact support.",
                "date_time": "2016-12-02T10:43:10Z",
                "type": "notification"
            }
        ],
        "ok": true
    }
}

Same considerations apply as for the system_messages call.

Flow

See Application Flow.

Authorization

In the scenario above, every instance in the discovery file runs their own OAuth server, so for each instance a new token needs to be obtained.

In order to support sharing access tokens between instances, e.g. for guest usage, we introduce three "types" of authorization:

local: every instance has their own OAuth server;
federated: there is one central OAuth server, all instances accept tokens from this OAuth server;
distributed: there is no central OAuth server, tokens from all instances can be used at all (other) instances.

The authorization_type key indicates which type is used. The supported values are local, federated or distributed mapping to the three modes described above.

Local

See API Discovery section above for determining the OAuth endpoints. The application MUST store the obtained access token and bind it to the instance the token was obtained from. If a user wants to use multiple VPN instances, a token MUST be obtained from all of them individually.

Federated

Here there is one central OAuth server that MUST be used. The OAuth server is specified in the discovery file in the authorization_endpoint and token_endpoint keys. When API discovery is performed, the keys for authorization_endpoint and token_endpoint for the specific instance MUST be ignored. Refreshing access tokens MUST also be done at the central server.

Distributed

Obtaining an access token from any of the instances listed in the discovery file is enough and can then be used at all the instances. Typically the user has the ability to obtain only an access token at one of the listed instances, because only there they have an account, so the user MUST choose first which of the instances they have an account at.

This is a bit messy from a UX perspective, as the user does not necessarily know for which instance they have an account. In case of eduVPN this will most likely be the instance operated in their institute's home country. So students of the University of Amsterdam will have to choose "The Netherlands" first.

When API discovery is performed, the keys for authorization_endpoint and token_endpoint for the specific instance MUST be ignored. Refreshing access tokens MUST also be done at the original OAuth server that was used to obtain the access token.

Caching

There are two types of discovery:

Instance Discovery
API Discovery

Both are JSON files that can be cached. It MUST be possible for the user to trigger a reload, i.e. get new copies of the cached files. This can be implemented for example using a button, or at the very least, an application restart.

The Instance Discovery files are also signed using public key cryptography, the signature MUST be verified and the value of the seq key of the verified file MUST be >= the cached copy. It MUST NOT be possible to "rollback", so for the instances discovery the cached copy MUST be retained.

The API discovery files do not currently have a signature and seq key, but MAY in the future.

Changelog

In API version 2, some calls were added:

POST to /create_keypair to create a private_key and certificate for an instance to be used with all profiles. This makes it possible to use one key pair per instance;
GET to /profile_config to obtain only the configuration file, without generating a key pair. This means the configuration can easily be refetched in case an update is needed without creating a new key pair;
GET to /user_info to obtain user information;
Extended authorization model in "Authorization" section.

For security reasons, API 2 switches to the authorization code flow, together with mitigations described in the following documents:

OAuth 2.0 for Native Apps (use latest version of specification);
Proof Key for Code Exchange by OAuth Public Clients

In particular, the use of PKCE is enforced, and the response_type MUST be code for the authorization request.

In version 2, the instances.json is also signed, so the signature MUST be validated by the consuming client.

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Introduction

Standards

Definitions

Instance Discovery

Validation

API Discovery

Authorization Request

Using the API

Profile List

User Info

Create a Configuration

Create a Key Pair

Profile Config

System Messages

User Messages

Flow

Authorization

Local

Federated

Distributed

Caching

Changelog

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Introduction

Standards

Definitions

Instance Discovery

Validation

API Discovery

Authorization Request

Using the API

Profile List

User Info

Create a Configuration

Create a Key Pair

Profile Config

System Messages

User Messages

Flow

Authorization

Local

Federated

Distributed

Caching

Changelog