@sap/xssec

3.6.1 • Public • Published

@sap/xssec: XS Advanced Container Security API for node.js

XS Advanced Authentication Primer

Authentication for node applications in XS Advanced relies on a special usage of the OAuth 2.0 protocol, which is based on central authentication at the UAA server that then vouches for the authenticated user's identity via a so-called OAuth Access Token. The current implementation uses as access token a JSON web token (JWT), which is a signed text-based token following the JSON syntax.

Normally, your node application will consist of several parts, that appear as separate applications in your manifest file, e.g. one application part that is responsible for the HANA database content, one application part for your application logic written e.g. in node.js (this is the one that can make use of this XS Advanced Container Security API for node.js), and finally one application part that is responsible for the UI layer (this is the one that may make use of the application router functionality). The latter two applications (the application logic in node.js and the application router) should be bound to one and the same UAA service instance. This has the effect, that these two parts can use the same OAuth client credentials.

When your business users access your application UI with their browser, the application router redirects the browser to the UAA where your business users need to authenticate. After successful authentication, the UAA sends - again via the business user's browser - an OAuth authorization code back to the application router. Now the application router sends this authorization code directly (not via the browser) to the UAA to exchange it into an OAuth access token. If the access token is obtained successfully, the business user has logged on to the UI part of your application already. In order to enable your UI to pass this authentication on to the node.js application part, you need to ensure that the destination to your node.js application part is configured such that the access token is actually sent to the node.js part ("forwardAuthToken": true).

In order to authenticate this request, which arrives at the node.js backend, sap-xssec offers two mechanisms: Firstly, you can use the XS Advanced Container Security API directly to validate the access token. Secondly, you can make use of the passport strategy that is contained in module sap-xssec as another convenient way how to handle the access token. In the following, both options are described followed by the sap-xssec API description.

sap-xssec offers an offline validation of the access token, which requires no additional call to the UAA. The trust for this offline validation is created by binding the XS UAA service instance to your application. Inside the credentials section in the environment variable VCAP_SERVICES, the key for validation of tokens is included. By default, the offline validation check will only accept tokens intended for the same OAuth2 client in the same UAA identity zone. This makes sense and will cover the vast majority of use cases.

If you want to enable another (foreign) application to use some of your application's scopes, you can add a granted-apps marker to your scope in the xs-security.json file (as in the following example). The value of the marker is a list of applications that is allowed to request a token with the denoted scope.

{
  "xsappname"     : "sample-leave-request-app",
  "description"   : "This sample application demos leave requests",
  "scopes"        : [ { "name"                : "$XSAPPNAME.createLR",
                        "description"         : "create leave requests" },
                      { "name"                : "$XSAPPNAME.approveLR",
                        "description"         : "approve leave requests",
                        "granted-apps"        : ["MobileApprovals"] }
                    ],
  "attributes"    : [ { "name"                : "costcenter",
                        "description"         : "costcenter",
                        "valueType"           : "string"
                    } ],
  "role-templates": [ { "name"                : "employee",
                        "description"         : "Role for creating leave requests",
                        "scope-references"    : [ "$XSAPPNAME.createLR","JobScheduler.scheduleJobs" ],
                        "attribute-references": [ "costcenter"] },
                      { "name"                : "manager",
                        "description"         : "Role for creating and approving leave requests",
                        "scope-references"    : [ "$XSAPPNAME.createLR","$XSAPPNAME.approveLR","JobScheduler.scheduleJobs" ],
                        "attribute-references": [ "costcenter" ] }
                    ]
}

Usage of the XS Advanced Container Security API in your node.js Application

In order to use the capabilities of the XS Advanced container security API, add the module "sap-xssec" to the dependencies section of your application's package.json.

To enable tracing, you can set the environment variable DEBUG as follows: DEBUG=xssec:*.

Direct Usage with existing Access Token

For the usage of the XS Advanced Container Security API it is necessary to pass a JWT token. If you have such a token, you may use the API as follows. The examples below rely on users and credentials that you should substitute with the ones in your context. The code below is based on version v0.0.9 (if you use another version, the coding might differ).

The typical use case for calling this API lies from within a container when an HTTP request is received. In an authorization header (with keyword bearer) an access token is contained already. You can remove the prefix bearer and pass the remaining string (just as in the following example as access_token) to the API.

xssec.createSecurityContext(access_token, xsenv.getServices({xsuaa:{tag:'xsuaa'}}).xsuaa, function(error, securityContext, tokenInfo) {
    if (error) {
        console.log('Security Context creation failed');
        return;
    }
    console.log('Security Context created successfully');
    console.log(tokenInfo.getPublicClaims());
});

Note that the example above uses module xsenv to retrieve the configuration of the default services (which are read from environment variable VCAP_SERVICES or if not set, from the default configuration file). However, it passes only the required uaa configuration to the method createSecurityContext. As default the UAA configuration is searched with tag xsuaa by xsenv. For details we refer to module @sap/xsenv. The xsenv documentation also helps if you want to provide the credentials from e.g. a user provided service.

The creation function xssec.createSecurityContext is to be used for an end-user token (e.g. for grant_type password or grant_type authorization_code) where user information is expected to be available within the token and thus within the security context.

createSecurityContext also accepts a token of grant_type client_credentials. This leads to the creation of a limited SecurityContext where certain functions are not available. For more details please consult the API description below or your documentation.

With version 3.1.0 there is a support for multiple configuration objects for one SecurityContext. For more details have a look here.

Support for X-Correlation-ID header

The xssec library internally calls REST APIs of the XSUAA. Now it's possible to set a correlationId during context creation and for token exchange calls. For this you have to restructe the configuration object.

const config = {
  credentials: xsenv.getServices({xsuaa:{tag:'xsuaa'}}).xsuaa,
  correlationId: "1111-1111-11111111"
};

//now you can call the createSecurityContext method as always
xssec.createSecurityContext(access_token, config, function(error, securityContext, tokenInfo) {
    if (error) {
        console.log('Security Context creation failed');
        return;
    }
    console.log('Security Context created successfully');
    console.log(tokenInfo.getPublicClaims());
});

Usage with Passport Strategy

If you use express and passport, you can easily plug a ready-made authentication strategy.

Since version 3.1.1 the JWTStratgy also supports the scope validation specified in passport.

var express = require('express');
var passport = require('passport');
var JWTStrategy = require('@sap/xssec').JWTStrategy;
var xsenv = require('@sap/xsenv');

...

var app = express();

...

passport.use(new JWTStrategy(xsenv.getServices({xsuaa:{tag:'xsuaa'}}).xsuaa));

app.use(passport.initialize());
app.use(passport.authenticate('JWT', { session: false }));

If JWT token is present in the request and it is successfully verified, following objects are created:

  • request.user - according to User Profile convention
    • id
    • name
      • givenName
      • familyName
    • emails [ { value: <email> } ]
  • request.authInfo - the Security Context
  • request.tokenInfo - the TokenInfo object

If the client_credentials JWT token is present in the request and it is successfully verified, following objects are created:

Session

It is recommended to disable the session as in the example above. In XSA each request comes with a JWT token so it is authenticated explicitly and identifies the user. If you still need the session, you can enable it but then you should also implement user serialization/deserialization and some sort of session persistency.

JWKS cache configuration

To verify the validity of a token, the library needs to ensure that it was signed with a public key from the authorization server's JWKS (JSON Web Key Set). The application retrieves the JWKS via HTTP from the authorization server. It is cached to reduce both the load on the authorization server and the latency of requests introduced by the token validation.

There are two values that are used to control the cache:

  • expiration time: When a JWKS is needed for validation whose cache entry has expired (time since last refresh > X), a refresh of the JWKS is performed (if not already in progress) and the token validation of the request needs to wait synchronously until the JWKS has been succesfully refreshed.
  • refresh period: When a JWKS is needed for validation whose cache entry is within the refresh period (time until expiration < Y), the cached JWKS will be used for validation (unless it has expired completely) and the JWKS will be refreshed asynchronously in the background.

Only one HTTP request at a time will be performed to refresh the JWKS.

In effect, productive systems with regular incoming requests should not experience delays from refreshing the JWKS (apart from the first request). Delays will only happen when the JWKS could not be refreshed during the refresh period, e.g. due to a prolonged outage of the JWKS endpoint or when no requests were received during the refresh period that would trigger a refresh.

Default cache configuration
{
  "expirationTime": 1800000, // 1800000ms = 30min
  "refreshPeriod": 900000, // 900000ms = 15min
}
Manual cache configuration

In rare situations you might need to change the cache configuration. The expiration time is important to support key rotation scenarios and should not be too high. Otherwise, the security of the application is impacted.

Normally you don't need to overwrite the default values!

To overwrite cache parameters you need to specify them as key/value pairs under <serviceCredentialJSON>.jwksCache. Please note that the cache parameters are configured in ms (milliseconds).

Example code:

// load service config
let config = xsenv.getServices({xsuaa:{tag:'xsuaa'}}).xsuaa;

// add a jwksCache object to the config
config.jwksCache = {
  expirationTime: 3600000
  refreshPeriod: 1800000,
};

// you can also overwrite only one value:
config.jwksCache = {
  refreshPeriod: 1200000,
};

// pass the config object to createSecurityConfig ...
xssec.createSecurityContext(access_token, config, function(error, securityContext, tokenInfo) {
   ...
});

// ... or if you use passport:
passport.use(new JWTStrategy(config));
...

x5t Token Validation

The library optionaly supports token ownership validation via x5t thumbprint (RFC 8705) for tokens issues by SAP Identity service.

❕ x5t token validation should only be enabled for applications using mTLS because the x5t validation will fail when there is no client certificate used for the request. SAP BTP will automatically put the client certificate in the x-forwarded-client-cert header of requests performed against cert application routes. From there it will be picked up by this lib to do the validation against the fingerprint claim from the token payload.

To enable x5t validation, pass a truthy value for the x5tValidation flag in the configuration object:

// when creating securityContext manually
xssec.createSecurityContext(access_token,
{ x5tValidation: true, x509Certificate: ... // PEM or DER encoded certificate as string
}, function(error, securityContext, tokenInfo) { ... });

// when using passport
app.use(passport.authenticate('JWT', { x5tValidation: true }));

Test Usage without having an Access Token

For test purposes, you may retrieve the token for a certain user (whose credentials you know) from the UAA as in the following code-snippet.

var http = require("http");
var xssec = require("@sap/xssec");
var xsenv = require('@sap/xsenv');
var request = require('request');

var uaaService = xsenv.getServices( { uaa: 'uaa' } ).uaa;
var testService = xsenv.getServices( { test : { label : 'test' } } ).test;
process.env.XSAPPNAME = testService.test.xsappname;

var options = {
    url : uaaService.url + '/oauth/token?client_id=' + uaaService.clientid
            + '&grant_type=password&username=' + testService.userid + '&password='
            + testService.usersecret
};
request.get(
    options,
    function(error, response, body) {
        if (error || response.statusCode !== 200) {
            console.log('Token request failed');
            return;
        }

        var json = null;
        try {
            json = JSON.parse(body);
        } catch (e) {
        	return callback(e);
        }

        xssec.createSecurityContext(json.access_token, uaaService, function(error, securityContext, tokenInfo) {
            if (error) {
                console.log('Security Context creation failed');
                return;
            }
            console.log('Security Context created successfully');
            console.log(tokenInfo.getPublicClaims());
        });
    }
).auth(uaaService.clientid, uaaService.clientsecret, false);

Note that this example assumes additional test configuration in the file default-services.json.

{
  "uaa": {
    "url"             : "<UAA URL>",
    "clientid"        : "<your application's OAuth client id>",
    "clientsecret"    : "<your application's OAuth client secret>",
    "xsappname"       : "<your application's name>",
    "identityzone"    : "<desired UAA identity zone>",
    "tags"            : ["xsuaa"],
    "verificationkey" : "<verification key for offline validation>"
  },
  "test": {
    "userid"          : "marissa",
    "usersecret"      : "koala"
  }
}

Support for X.509 authentication for token exchange

XSUAA offers the possibility to use X.509 authentication. Since version 3.2.2 the node-xssec library supports to use this.

As a developer you normally do not need to do something differently. You create a SecurityContext with the configuration object you get from the environment. If the XSUAA is configured to use X.509 the config object does not contain a clientsecret. Instead of this, there are a certificate and a key attributes. The library will use these attributes during token exchanges to fetch the tokens from xsuaa using mtls.

X.509 with XSUAA managed certificates

If your XSUAA instance is configured to manage certificates and keys on its own, you can take the configuration object from VCAP services and pass it to the createSecurityContext method. The needed certificate and key attributes are already filled.

There is no difference to client-credential based token exchange.

X.509 with external certificates

If you configured your XSUAA instance to use an external managed certificate/key you need to provide the key attribute to the configuration object.

For this you take the JSON from VCAP-Services and add the PEM encoded key as a string to the configuration.

//read xsuaa config from VCAP
const config = xsenv.getServices({xsuaa:{tag:'xsuaa'}}).xsuaa;

const myExternalManagedKey = "-----BEGIN RSA PRIVATE KEY-----...-----END RSA PRIVATE KEY-----\n";
config.key = myExternalManagedKey;

//if using passport
passport.use(new JWTStrategy(config));

//or create a security context directly
xssec.createSecurityContext(access_token, config, function(error, securityContext, tokenInfo) {
    //now you can run a tokenExchange with the provided key    
    xssec.requestToken(config, constants.TYPE_USER_TOKEN, null, function(err, data) {

    })    
});

Usage in Docker

In versions <= 3.0.0 there was no support for alpine base images. But since verion >= 3.0.0 the xssec library has no dependency to a native library anymore. So it is now fully compatible with alpine images.

API Description

createSecurityContext

This function creates the Security Context by validating the received access token against credentials put into the application's environment via the UAA service binding.

Usually, the received token must be intended for the current application. More clearly, the OAuth client id in the access token needs to be equal to the OAuth client id of the application (from the application's environment).

Parameters:

  • access token ... the access token as received from UAA in the "authorization Bearer" HTTP header
  • config ... a structure with mandatory elements url, clientid and clientsecret or cache configuration. Since version 3.1.0 it may also be an array of these structures (have a look here)
  • callback(error, securityContext, tokenInfo)

getLogonName

not available for tokens of grant_type client_credentials, returns the logon name

getGivenName

not available for tokens of grant_type client_credentials, returns the given name

getFamilyName

not available for tokens of grant_type client_credentials, returns the family name

getEmail

not available for tokens of grant_type client_credentials, returns the email

getUserName

returns unique principal name of a user user/<origin>/<logon name> or client id that the access token has been issued for client/<client id>

getUniquePrincipalName

not available for tokens of grant_type client_credentials, returns unique principal name of a user. user/<origin>/<logon name>

getOrigin

  • returns the user origin. The origin is an alias that refers to a user store in which the user is persisted. For example, users that are authenticated by the UAA itself with a username/password combination have their origin set to the value uaa.

checkLocalScope

checks a scope that is published by the current application in the xs-security.json file.

Parameters:

  • scope ... the scope whose existence is checked against the available scopes of the current user. Here, no prefix is required.
  • returns true if the scope is contained in the user's scopes, false otherwise

checkFollowingInstanceScope

checks a instance specific scope that is published by the current application in the xs-security.json file. Use this to check a scope from a service instance.

Parameters:

  • scope ... the scope whose existence is checked against the available scopes of the current user. Here, no prefix is required.
  • returns true if the scope is contained in the user's scopes, false otherwise

checkScope

checks a scope that is published by an application.

Parameters:

  • scope ... the scope whose existence is checked against the available scopes of the current user. Here, the prefix is required, thus the scope string is "globally unique".
  • returns true if the scope is contained in the user's scopes, false otherwise

getAppToken

  • returns the token of the application that can be used e.g. for token forwarding to another app.

getHdbToken

  • returns a token that can be used for contacting the HANA database. If the token, that the security context has been instantiated with, is a foreign token (meaning that the OAuth client contained in the token and the OAuth client of the current application do not match), null is returned instead of a token.

getTokenInfo

  • returns the TokenInfo object, containing all information received from token.

requestToken

Requests a token based on the given type. The type can be constants.TYPE_USER_TOKEN or constants.TYPE_CLIENT_CREDENTIALS_TOKEN.

  • serviceCredentials ... the credentials of the service as JSON object. The attributes clientid, clientsecret and url (UAA) are mandatory. Note that the subdomain of the url will be adapted to the subdomain of the application token if necessary.
  • type ... allowed values are constants.TYPE_USER_TOKEN and constants.TYPE_CLIENT_CREDENTIALS_TOKEN
  • additionalAttributes ... the attributes that should be included into the JWT token as JSON object (key-value list), e.g. {"attr1" : "value1", "attr2" : "value2"}
  • cb(error, token) ... callback function

also have a look on how to initiate the token flows directly

hasAttributes

not available for tokens of grant_type client_credentials.

  • returns true if the token contains any xs user attributes, false otherwise.

getAttribute

not available for tokens of grant_type client_credentials.

Parameters:

  • name ... The name of the attribute that is requested.
  • returns the attribute exactly as it is contained in the access token. If no attribute with the given name is contained in the access token, null is returned. If the token, that the security context has been instantiated with, is a foreign token (meaning that the OAuth client contained in the token and the OAuth client of the current application do not match), null is returned regardless of whether the requested attribute is contained in the token or not.

getAdditionalAuthAttribute

Parameters:

  • name ... The name of the additional authentication attribute that is requested.
  • returns the additional authentication attribute exactly as it is contained in the access token. If no attribute with the given name is contained in the access token, null is returned. Note that additional authentication attributes are also returned in foreign mode (in contrast to getAttribute).

isInForeignMode

  • returns true if the token, that the security context has been instantiated with, is a foreign token that was not originally issued for the current application, false otherwise.

getSubdomain

  • returns the subdomain that the access token has been issued for.

getClientId

  • returns the client id that the access token has been issued for.

getSubaccountId

  • returns the subaccount id that the access token has been issued for.

getZoneId

  • returns the identity zone that the access token has been issued for.

getExpirationDate

  • returns the expiration date of the access token as javascript Date object.

getCloneServiceInstanceId

  • returns the service instance id of the clone if the XSUAA broker plan is used.

getGrantType

  • returns the grant type of the JWT token, e.g. authorization_code, password, client_credentials or urn:ietf:params:oauth:grant-type:saml2-bearer.

Latest published Version

Use this command to check for the latest version that is published to the NPM repository:

npm view --registry https://npm.sap.com @sap/xssec versions

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