(PureBasic) Verify a JWT Created by the Amazon Cognito Service

Demonstrates how to verify a JWT created by the Amazon Cognito Service.

Chilkat PureBasic Module Download Chilkat PureBasic Module

IncludeFile "CkHttp.pb"
IncludeFile "CkStringBuilder.pb"
IncludeFile "CkJsonObject.pb"
IncludeFile "CkPublicKey.pb"
IncludeFile "CkJwt.pb"

Procedure ChilkatExample()

    ; This example requires the Chilkat API to have been previously unlocked.
    ; See Global Unlock Sample for sample code.

    ; The public keys for this example are at https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json
    ; Let's get them:

    http.i = CkHttp::ckCreate()
    If http.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    sbJsonKeys.i = CkStringBuilder::ckCreate()
    If sbJsonKeys.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success.i = CkHttp::ckQuickGetSb(http,"https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json",sbJsonKeys)
    If success = 0
        Debug CkHttp::ckLastErrorText(http)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbJsonKeys)
        ProcedureReturn
    EndIf

    jsonKeys.i = CkJsonObject::ckCreate()
    If jsonKeys.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    CkJsonObject::ckLoadSb(jsonKeys,sbJsonKeys)
    CkJsonObject::setCkEmitCompact(jsonKeys, 0)
    Debug CkJsonObject::ckEmit(jsonKeys)

    ; Here are the keys:

    ; {
    ;   "keys": [
    ;     {
    ;       "alg": "RS256",
    ;       "e": "AQAB",
    ;       "kid": "1A/L5Fsb2EsEwxy5E0cmCMS1BnMe6Jl6NXiMig4iNwU=",
    ;       "kty": "RSA",
    ;       "n": "y0w7BJrIJYi ... jKG27z2P3OKw",
    ;       "use": "sig"
    ;     },
    ;     {
    ;       "alg": "RS256",
    ;       "e": "AQAB",
    ;       "kid": "mos6VTJnvDwurY3ghJg6IAPUq+dMwl6CL/iThzJOkzg=",
    ;       "kty": "RSA",
    ;       "n": "qbIEH-7tg6yrT ... 3Fj94ooTd0w",
    ;       "use": "sig"
    ;     }
    ;   ]
    ; }

    ; Try the 1st key.
    jsonKey1.i = CkJsonObject::ckObjectOf(jsonKeys,"keys[0]")
    If CkJsonObject::ckLastMethodSuccess(jsonKeys) = 0
        Debug "Did not get the 1st JSON public key."
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbJsonKeys)
        CkJsonObject::ckDispose(jsonKeys)
        ProcedureReturn
    EndIf

    pubKey1.i = CkPublicKey::ckCreate()
    If pubKey1.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkPublicKey::ckLoadFromString(pubKey1,CkJsonObject::ckEmit(jsonKey1))
    If success = 0
        Debug CkPublicKey::ckLastErrorText(pubKey1)
        CkHttp::ckDispose(http)
        CkStringBuilder::ckDispose(sbJsonKeys)
        CkJsonObject::ckDispose(jsonKeys)
        CkPublicKey::ckDispose(pubKey1)
        ProcedureReturn
    EndIf

    CkJsonObject::ckDispose(jsonKey1)

    Debug "Success"

    jwt.i = CkJwt::ckCreate()
    If jwt.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    ; I did not include the an actual AWS Cognito token here because our test sample used customer-provided data..
    token.s = "eyJ..asXg"

    ; First verify the signature.
    sigVerified.i = CkJwt::ckVerifyJwtPk(jwt,token,pubKey1)
    Debug "verified: " + Str(sigVerified)

    ; Let's see if the time constraints, if any, are valid.
    ; The above JWT was created on the afternoon of 16-May-2016, with an expiration of 1 hour.
    ; If the current system time is before the "nbf" time, or after the "exp" time,
    ; then IsTimeValid will return false/0.
    ; Also, we'll allow a leeway of 60 seconds to account for any clock skew.
    ; Note: If the token has no "nbf" or "exp" claim fields, then IsTimeValid is always true.
    leeway.i = 60
    bTimeValid.i = CkJwt::ckIsTimeValid(jwt,token,leeway)
    Debug "time constraints valid: " + Str(bTimeValid)

    ; Now let's recover the original claims JSON (the payload).
    payload.s = CkJwt::ckGetPayload(jwt,token)
    ; The payload will likely be in compact form:
    Debug payload

    ; We can format for human viewing by loading it into Chilkat's JSON object
    ; and emit.
    json.i = CkJsonObject::ckCreate()
    If json.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    success = CkJsonObject::ckLoad(json,payload)
    CkJsonObject::setCkEmitCompact(json, 0)
    Debug CkJsonObject::ckEmit(json)

    ; We can recover the original JOSE header in the same way:
    joseHeader.s = CkJwt::ckGetHeader(jwt,token)
    ; The payload will likely be in compact form:
    Debug joseHeader

    ; We can format for human viewing by loading it into Chilkat's JSON object
    ; and emit.
    success = CkJsonObject::ckLoad(json,joseHeader)
    CkJsonObject::setCkEmitCompact(json, 0)
    Debug CkJsonObject::ckEmit(json)


    CkHttp::ckDispose(http)
    CkStringBuilder::ckDispose(sbJsonKeys)
    CkJsonObject::ckDispose(jsonKeys)
    CkPublicKey::ckDispose(pubKey1)
    CkJwt::ckDispose(jwt)
    CkJsonObject::ckDispose(json)


    ProcedureReturn
EndProcedure