August 13, 2019

JWTs in Sitecore XC9 🔐

Sitecore XC9 uses JSON Web Tokens (JWTs) for authentication & authorization. JWTs are well explained here. In this blog post we investigate how JWTs are configured and handled in the Sitecore Identity Server and Commerce Engine.

In this article Jonne Kats gives a nice overview of how authentication and authorization works in XC9. The Bearer token authentication variant uses a token: a JSON Web Token (JWT).

Obtain and inspect JWT

A token is retrieved from the Identity Server using the https://identity/connect/token endpoint by providing approriate username and password credentials (assuming you use the password grant type). An example JWT looks like:

{
    "access_token": "eyJhbGciOiJSUzI1NiIsImtpZCI6IjZFQjhFMDg3NjhBNjg2M0VCMUIzMTQ3NTEwMjdDMjVEQzhFMDYwOUQiLCJ0eXAiOiJKV1QiLCJ4NXQiOiJicmpnaDJpbWhqNnhzeFIxRUNmQ1hjamdZSjAifQ.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.kwsUFFkIByy3jTC3vr7gmlCdbtH9tt4A9pz0mBDzCr8t1CawW9owDCxjgAXEPsydFAPXEcebiVnldqf1bgVMOhHBhi14lhBH2lbsXx-GuwSBE5wbIrCf3DcO-cFQDixQAsU0GeUuLV3_okmY84em-Se_dicsLcPs65L-L75DRw5JgdkRZgUrzAjsnny8aLNrfMR2F8VYviHMpB5p-76OiIuIVr2KWmsa5qvZSX1LeFRr6xzACE276rl4cH-fb56PwOS-EW8i_Tdr4QIZUiOAIvdbpBUTQvZiA-RFKqFFGcNMqBooKWvIQcqMlo4FH2SrthO-hRvEAPvBSgvS52c56Q",
    "expires_in": 3600,
    "token_type": "Bearer"
}

The JWT contains an access_token with the <header>.<payload>.<signature> format. You can use https://jwt.io to decode the JWT. After decoding the header and payload of the JWT are visible, a decoded example payload:

{
  "nbf": 1565633364,
  "exp": 1565636964,
  "iss": "https://identity",
  "aud": [
    "https://identity/resources",
    "EngineAPI",
    "postman_api"
  ],
  "client_id": "postman-api",
  "sub": "e27df215a10b4d4e86ee3a2a67539ca9",
  "auth_time": 1565633364,
  "idp": "local",
  "name": "sitecore\\Admin",
  "email": "",
  "role": [
    "sitecore\\Commerce Administrator",
    "sitecore\\Customer Service Representative Administrator",
    "sitecore\\Customer Service Representative",
    "sitecore\\Commerce Business User",
    "sitecore\\Pricer Manager",
    "sitecore\\Pricer",
    "sitecore\\Promotioner Manager",
    "sitecore\\Promotioner",
    "sitecore\\Merchandiser",
    "sitecore\\Relationship Administrator"
  ],
  "scope": [
    "openid",
    "EngineAPI",
    "postman_api"
  ],
  "amr": [
    "pwd"
  ]
}

The above payload contains information that was issued by the Identity Server, e.g. amr for the used authentication method and role for the roles assigned to the user.

Verify JWT

The public key to verify the JWT is defined using a JSON Web Key Set (JWKS). The Identity Server exposes a JWKS at https://identity/.well-known/openid-configuration/jwks. The public key (e.g. certificate) is available in the x5c field.

To verify a JWT the Commerce Engine uses the public key from the JWKS.

In C# code JWT authentication is configured in Startup.cs of the Commerce Engine:

public void ConfigureServices(IServiceCollection services)
{
    ...

    services.AddAuthentication(options =>
    {
        options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
        options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
    })
    .AddIdentityServerAuthentication(options =>
    {
        options.Authority = this.Configuration.GetSection("AppSettings:SitecoreIdentityServerUrl").Value;
        options.RequireHttpsMetadata = false;
        options.EnableCaching = false;
        options.ApiName = "EngineAPI";
        options.ApiSecret = "secret";
    });

    ...
}

Note that AddIdentityServerAuthentication is an extension method and contains (see here) the configuration that is described in the Identity Server documentation: http://docs.identityserver.io/en/latest/topics/apis.html

Furthermore it seems that the default Commerce Engine implementation, which only uses JWT tokens and not Reference tokens, defines some unused settings (e.g. ApiSecret): https://sitecore.stackexchange.com/questions/20445/should-i-harden-commerce-engine-apisecret

Verify JWT

A JWT can verified online at https://jwt.io/. You need to supply a public and private key.

The public key can be obtained from the JWKS or directly from the PFX certificate:

openssl pkcs12 -in <filename>.pfx -clcerts -nokeys -out cert.pem

The private key has to be extracted from the PFX file:

openssl pkcs12 -in <filename>.pfx  -nocerts -out key.pem

Copy-paste the public and private keys from the x5c property (or cert.pem) and key.pem into the verify RSASHA256 signature fields in https://jwt.io/.

If everything went well you should see a Valid Signature message.

Identity Server Configuration

The certificate to use for JWT signing is defined in Config/production/Sitecore.IdentityServer.Host.xml.

It contains, amongst other settings, the certificate to use for signing e.g:

<Settings>
  <Sitecore>
    <IdentityServer>
      <CertificateThumbprint>6EB8E08768A6863EB1B314751027C25DC8E0609D</CertificateThumbprint>
      <CertificateStoreLocation>LocalMachine</CertificateStoreLocation>
      <CertificateStoreName>My</CertificateStoreName>
      ...
    </IdentityServer>
  </Sitecore>
</Settings>

NB. the certificate thumbprint corresponds with the kid (key id) in the JWKS.

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© Joost Meijles 2019

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