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Note that this documentation only describes the protocol to get the EAP metadata. Anything to do with mobile is not yet documented.

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As an overview on how a Geteduroam app/client does this is the following:

  • The app starts up
  • A Discovery file is obtained that lists each instance and their way to get the EAP metadata. This file is gotten from a discovery server, it is possible that clients implement caching using a local copy
  • This discovery file is parsed to list all the instances in it. This discovery file is parsed using JSON
  • The user selects an instance either by clicking on one or filtering on it using a search box
  • The selected instance is used to obtain the EAP metadata, either through OAuth or directly getting the configuration. It is possible that instead of getting the EAP metadata, the user is redirected to a webpage that handles the further setup
  • The EAP metadata is parsed, using XML. Validating that the EAP metadata is correct can be done through XML schemas
  • The app determines whether or not user provided credentials or secrets still need to be provided
  • When the user has entered these credentials, the eduroam profile can be configured in the OS network manager

Discovery format

Geteduroam uses https://discovery.eduroam.app/v1/discovery.json, a JSON file, to list all the institutes generated from CAT. This list is shown in a Geteduroam client so that the user can choose its own institution to connect to.

The script that generates this discovery JSON file can be found on the Geteduroam GitHub. The format of this JSON file is the following:

{
"instances": instances (list, required),
"seq": [YEAR][MONTH][DAY][UPDATE NUMBER] (integer, required); e.g. 2023020908, meaning: 2023, february 9, update 8),
"version": 1 (integer, required); always set to 1 right now,
}

The last part of the "seq" field is used to indicate the nth update of the day, starting at 0. If an old update cannot be found it starts at 80, see https://github.com/geteduroam/cattenbak/blob/481e243f22b40e1d8d48ecac2b85705b8cb48494/cattenbak.py#L115 for how it works in detail. It is currently undecided if clients should parse this to exactly match the format. In this client, we currently do this; meaning we parse the year month day and check for the update number. An alternative way is to parse this just as an integer without any meaning except that a newer version has a higher number.

To protect against rollback attacks, it is good practice to check the sequence number if it has updated.

Where instances is a list of the form:

    "cat_idp": cat identifier (integer, required); e.g. 7088,
    "country": country code (string, required); e.g. "RO",
    "geo": [
        "lat": latitude (float, required),
        "lon": longitude (float, required),
    ] (required),
    id: cat_id (string, required); e.g. "cat_7088",
    name: the name of the organisation to be shown in the UI (string, required); e.g. SURF,
    profiles: [
        "authorization_endpoint": The authorization endpoint in case OAuth is used (string, optional); e.g. "https://example.com/oauth/authorize/",
        "default": If this profile is the default profile (bool, optional); e.g. True,
        "eapconfig_endpoint": The endpoint to obtain the EAP config (string, required); e.g. "https://example.com/api/eap-config/",
        "id": The identifier of the profile (string, required); e.g. "letswifi_cat_1337",
        "name": The name of the profile to be shown in the UI; e.g. "Demo Server",
        "oauth": Whether or not OAuth is enabled. If missing, OAuth is not enabled (bool, optional); e.g. true,
        "token_endpoint": The endpoint to get OAuth tokens from (string, optional); e.g. "https://example.com/oauth/token/", 
    ] (required),

This instances list should be parsed by the client. The name of the instance is what is shown in the UI. Filtering on the instance is also done with this name. For example if an user searches for "sur", it would include "SURF" due to substring case-insensitive matching.

Variants/flows

As can be deduced from the instance format, there are various flows possible to configure the eduroam network with a certain profile:

  • Directly get the EAP config from the eapconfig_endpoint: eapconfig_endpoint, name, id and oauth (oauth set to False) MUST be present
  • Get the EAP config using tokens obtained through authorization_endpoint and token_endpoint using OAuth: eapconfig_endpoint, authorization_endpoint, token_endpoint, name, id and oauth (oauth set to True) MUST be present
  • Forward the user to a "redirect" page: id, name and redirect must be present

Based on the various presence and values of these attributes you can determine the flow as follows:

  • If redirect is present, then the redirect flow MUST be used
  • Else, check whether oauth is set to True then OAuth flow, else direct flow
    • For a more complete check, instead of only checking if oauth is True a client can also check for the presence of authorization_endpoint and token_endpoint

The implementation of each flow will be given later. Before we can do that, however, we first explain how a profile should be selected

Profile selection

As can be deduced from the JSON format, there are multiple profiles available per instance. If an instance only has one profile then the profile MUST be automatically chosen without any user interaction.

If there are multiple profiles then multiple profiles MUST be shown in the UI, asking for a selection to the user. The profile indicated with the default attribute set to true SHOULD be in bold, or in case the UI does not support bold text, it SHOULD have a */(default) pre/postfix.

When the profile has been selected, we can use the correct flow to get the EAP metadata. In the next section, we will go over implementing the various flows.

Flow implementations

This section describes the different way that the app should continue when the profile has been selected.

Redirect

After parsing the discovery entry and determining that the flow is Redirect, the redirect should be verified whether or not the following holds:

  • The value is a URL
  • The scheme of the URL is HTTPS or HTTP

If the value is not a URL, or the scheme is not HTTP/HTTPS, the app MUST NOT open the url in the browser but should show a friendly error in the UI that the profile is not available.

If the scheme of the URL is HTTP it MUST be rewritten to HTTPS.

Note that the redirect flow is one of the last steps that the app needs to do as the redirect does not give back an EAP metadata file. This redirect is only used to give the user information on how to proceed with configuring the network himself.

Direct

When the app has determined that the profile does not support redirect and oauth is disabled, the app should get the eap config via the eapconfig_endpoint. The EAP metadata file is returned in the HTTP response body.

Note that like the URL in redirect, the app MUST parse the eapconfig_endpont to check whether or not it is a valid URL, the scheme is HTTP or HTTPS and MUST rewrite HTTP to the HTTPS scheme.

OAuth

The extra fields that are available in the OAuth flow are the authorization_endpoint and the token_endpoint. We go over them one by one what should be done.

NOTE: The authorization endpoint and token endpoint docs is taken from https://www.geteduroam.app/developer/api/ and slightly modified

Authorization endpoint

Build a URL for the authorization endpoint; take the authorization_endpoint string from the discovery, and add the following GET parameters (MUST be implemented according to RFC6749 section 4.1.1 for most of these):

  • response_type (MUST be set to code)
  • code_challenge_method (MUST be set to S256)
  • scope (MUST be set to eap-metadata)
  • code_challenge (a code challenge)
  • redirect_uri (where the user should be redirected after accepting or rejecting your application, GET parameters will added to this URL by the server. MUST be local, e.g. http://127.0.0.1/callback)
  • client_id (MUST be your client ID as known by the server)
  • state (a random string that will be set in a GET parameter to the redirect_uri, for you to verify it’s the same flow))

You have created a URL, for example:

https://demo.eduroam.no/authorize.php?response_type=code&code_challenge_method=S256&scope=eap-metadata&code_challenge=E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM&redirect_uri=http%3A%2F%2Flocalhost%3A1080%2Fcallback&client_id=00000000-0000-0000-0000-000000000000&state=0

You open a local webbrowser to this URL on the users' device and listen on the redirect_uri for a request to return. Upon receiving a request, the client SHOULD reclaim focus to the application window and MUST handle the request. You may receive these GET parameters:

  • code (the authorization code that you can use on the token endpoint)
  • error (an error message that you can present to the user)
  • state (the same value as your earlier state GET parameter which MUST be checked)

As a reply to this request, you SHOULD simply return a message to the user stating that he should return to the application. Depending on the platform, you SHOULD also return code to trigger a return to the application.

Token endpoint

The token endpoint requires a code, which you obtain via the Authorization endpoint. Use the token_endpoint string from the discovery.

You need the following POST parameters:

  • grant_type (MUST be set to authorization_code)
  • code (MUST be the code received from the authorization endpoint)
  • redirect_uri (MUST repeat the value used in the previous request, as mandated by RFC7636)
  • client_id (MUST repeat the value used in the previous request, as mandated by RFC7636)
  • code_verifier (MUST be a code verifier, as documented in RFC7636 section 4. This is the preimage of the code challenge to prove that you are the original sender of the authorization endpoint request )

You get back a JSON dictionary, containing the following keys:

  • access_token
  • token_type (set to Bearer)
  • expires_in (validity of the access_token in seconds)

Example HTTP conversation

POST /token.php HTTP/1.1
Accept: application/json
Content-Type: application/x-www-form-urlencoded
Content-Length: 209

grant_type=authorization_code&code=v2.local.AAAAAA&redirect_uri=http%3A%2F%2Flocalhost%3A1080%2Fcallback&client_id=00000000-0000-0000-0000-000000000000&code_verifier=dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

HTTP/1.1 200 OK
Cache-Control: no-store
Content-Type: application/json;charset=UTF-8
Pragma: no-cache

{
	"access_token": "v2.local.AAAAA…==",
	"token_type": "Bearer",
	"expires_in": 3600
}

Saving this access token SHOULD be done securely, e.g. in a keyring. This way the client can re-use this access token across restarts.

Doing the authorized request

Now that the client has retrieved the access token, it needs to get the EAP metadata using it. To do this, the client MUST send the access token in the authorization header when making a request to eapconfig_endpoint:

curl \
	-H "Authorization: Bearer SETTHETOKENHERE" \
	https://example.org/api/eap-config

Note that error handling on the HTTP code should done to accordance with RFC6749. In short, when the client gets a HTTP 401 here then that possibly means that the access token is expired or invalid/blacklisted. Therefore the client MUST check before it sends the request if the access token is still valid.

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