Additionally, non SQL, there is a built in function for this of

if ##class(Security.Users).Exists("John") {
    // user exists
}

which confirms if the IRIS user exists using the users username (here, assuming username of John). Documentation on the Security.Users docs page.

Hi Alin,

Looking in the Caché & Ensemble 2018.1.4 – 2018.1.9 documentation there is a class %OAuth2.JWKS with method AddOct() for Cache almost identical to the one you described above for IRIS. This method is available for Cache 2018.1.9 the version you listed in your question. Hope this documentation helps.

For others reference w.r.t. IRIS, the method and class you described above are deprecated in later versions of IRIS and %Net.JSON.JWK or %Net.JSON.JWKS should be used instead.