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About token signatures

This topic tells you about the concept of token signatures.

Token signature 101

Token signature keys are used by an AuthServer to sign JSON Web Tokens (JWTs), produce a JWS Signature and attach it to the JOSE Header of a JWT. The client application can then verify the JWT signature.

A private key signs a JWT. A public key verifies the signature of a signed JWT.

The sign-and-verify mechanism serves multiple security purposes:

  • Authenticity: signature verification ensures that the issuer of the JWT is from a source that is advertised.
  • Integrity: signature verification ensures that the JWT has not been altered in transit or during its issued lifetime. Integrity is a foundational pillar of the CIA triad concept in Information Security.
  • Non-repudiation: signature verification ensures that the authorization server that signed the JWT cannot deny that they have signed it after its issuance (granted that the signing key that signed the JWT is available).

AppSSO only supports the RS256 algorithm for signing tokens. For more information, see JSON Web Algorithms (JWA) documentation.

Token signature of an AuthServer

You must configure token signatures for AuthServer. An AuthServer receives its keys under spec.tokenSignature. For example:

spec:
  tokenSignature:
    signAndVerifyKeyRef:
      name: sample-token-signing-key
    extraVerifyKeyRefs:
      - name: sample-token-verification-key-1
      - name: sample-token-verification-key-2

There can only be one token signing key spec.tokenSignature.signAngVerifyKeyRef at any given time, and arbitrarily many token verification keys spec.tokenSignature.extraVerifyKeyRefs. The token signing key is used to sign and verify actively issued JWTs in circulation, whereas token verification keys are used to verify issued JWTs signatures. Token verification keys are thought to be previous token signing keys but have been rotated into verify only mode as a rotation mechanism measure, and can potentially be slated for eviction at a predetermined time.

The AuthServer serves its public keys at {spec.issuerURI}/oauth2/jwks. For example:

$ curl -s authserver-sample.default/oauth2/jwks | jq
{
  "keys": [
    {
      "kty": "RSA",
      "e": "AQAB",
      "kid": "sample-token-signing-key",
      "n": "0iCinir7sWKZE_3QXq4eTub_GU-lvdAKFI9dzDlwX7XZwwSERuzzQQ_Fs7i9djMl5bpv2ma_3ZB-j2W9pR9ZIa3nqBI29AHqx2zmVQ8w-GxPDGRMkBdMOWNwyDQGIRlQnJFpXRoSQ5_viM9gYA56WthkDghrupGUiB_zqGFYlgnz7sd4lC-thgEkDi9vY68DLIFdsXOQIXFqakyEIo43n_0vg6JRGQW1LU_32Ok6OgA3r6bYcE8VQhJW3sE1qOSFcP0JrPA3YgmTNuDV6GoCLZeMxDdMDKdDcH5UgERLQe1qMMKwlMCeKamOWgo9eBvcFnWNR0I_MJV6F14U1WbIcQ"
    },
    {
      "kty": "RSA",
      "e": "AQAB",
      "kid": "sample-token-verification-key-1",
      "n": "wc7uOACU62Yu_zKT9YrI4v-_X3L47nbVlcByi4UTVhg8o001OkiYAPAEoDCEHnDg_54gTWxe3hDRcOJrd72PkTAaxH8aFdikoyakRVG9NvAPbcfzvI8R8plepUbs1U7TPPDEDARm_fZX6QdVyz0CTSafrz-yktTADxJhYPgvFLeHq7g7RouB1szTWDCM1haoxKa4960_x9meghNn87z0uF3cAd7TM_k3capYnxNOUT5g1vjJ05Vk14JUl4R294OpMXPCGcFuvu9auXeBqXyKxxTAnLkDdNrgtT0FJHwnh4RGnrNqjYZOwlRvGbzwQ7du97aU2-qgbKkJrWYZWcw2bQ"
    },
    {
      "kty": "RSA",
      "e": "AQAB",
      "kid": "sample-token-verification-key-2",
      "n": "qELrLiaD-IVp_nthVn2EsLuShtU9ovyVIPkLVf47AqKogPV2frE_6Sv8k7Zim-SgDXfjLEg-UGlQrb4KFm_WkaK2Uf6PCapiBnMi1Q5P8qC0WC5LT6XyPY1exCQbMrEsyd89oS0sKxgoc3Qv0XV24jGYiWQyJ7I0Rub_QEldGM_dSlfbI-1Qt_U6Ll22OEc1D6P1A3MdDrgbur6N7ZemxlKI26-OAdlbNi0u-lFNj3Ss-pfTVi_fD2hAajRRmc4tmHejQjH36M4F1NSW_gTbb6VX5EerVuDwSCCK0EuGvhcb1hg6kYEoO-qws54AQ0PywBXT5qksCMBmmzjP6qO4Ow"
    }
  ]
}

Caution Changes to spec.tokenSignature.signAngVerifyKeyRef have immediate effects.

As a service operator, you have control over which keys are used for certain purposes. For more information, see Manage token signature keys for Application Single Sign-On.