Encrypted Principal Id

Most if not all username attribute providers are able to encrypt the resolved username, assuming the service definition is given a public key.

The key can be generated via the following commands:

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openssl genrsa -out private.key 1024
openssl rsa -pubout -in private.key -out public.key -inform PEM -outform DER
openssl pkcs8 -topk8 -inform PEM -outform DER -nocrypt -in private.key -out private.p8

The public key is then configured for a service definition in CAS:

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{
  "@class" : "org.apereo.cas.services.CasRegisteredService",
  "serviceId" : "sample",
  "name" : "sample",
  "id" : 100,
  "description" : "sample",
  "usernameAttributeProvider" : {
    "@class" : "org.apereo.cas.services.DefaultRegisteredServiceUsernameProvider",
    "encryptUsername" : "true"
  },
  "publicKey" : {
    "@class" : "org.apereo.cas.services.RegisteredServicePublicKeyImpl",
    "location" : "classpath:public.key",
    "algorithm" : "RSA"
  }
}

The configuration of the public key component qualifies to use the Spring Expression Language syntax.

The application can then proceed to decrypt the username using its own private key. The following sample code demonstrates how that might be done in Java:

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var casUsername = ...
var privateKey = ...
var cipher = Cipher.getInstance(privateKey.getAlgorithm());
var cred64 = decodeBase64(encodedPsw);
cipher.init(Cipher.DECRYPT_MODE, privateKey);
var cipherData = cipher.doFinal(casUsername);
return new String(cipherData);