(Tcl) Verify Okta Access Token Locally

This example demonstrates how to validate an Okta access token using Chilkat's JWT class.

For more information, see https://developer.okta.com/docs/guides/validate-access-tokens/overview/#what-to-check-when-validating-an-access-token

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load ./chilkat.dll

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

# This example begins with two JSON files:
# 
# 1. The access token obtained from Okta as shown in one fo these examples:  
#    Get Okta Token using Resource Owner Password Flow
# 
# 2. The Okta web keys obtained by this example:  Get Okta Web Keys
# 
# 

# Load the access token to be verified.
# It contains JSON that looks like this:
# {
#   "access_token": "eyJraWQiOiJhb ... O_eVu-kBp6g",
#   "token_type": "Bearer",
#   "expires_in": 3600,
#   "scope": "openid",
#   "id_token": "eyJraWQi ... FrL9WOuwbQtUg"
# }
# This example verifies the access_token.  (The id_token is verified in this example:  Verify Okta ID Token

set jsonToken [new_CkJsonObject]

set success [CkJsonObject_LoadFile $jsonToken "qa_data/tokens/okta_access_token.json"]

# Load the public keys (Okta web keys), one of which is needed to validate.
# The web keys JSON looks like this:
# {
#   "keys": [
#     {
#       "kty": "RSA",
#       "alg": "RS256",
#       "kid": "anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ",
#       "use": "sig",
#       "e": "AQAB",
#       "n": "jT8uAgd5w ... euLB1HaVw"
#     },
#     {
# 	...
#     }
#   ]
# }

set jsonWebKeys [new_CkJsonObject]

set success [CkJsonObject_LoadFile $jsonWebKeys "qa_data/tokens/okta_web_keys.json"]

# ------------------------
# Step 1: Get the JOSE header from the JWT.  The JOSE header contains JSON.  One of the JSON members will be the key ID "kid" which identifies the web key to be used for validation.
# 
set jwt [new_CkJwt]

set accessToken [CkJsonObject_stringOf $jsonToken "access_token"]
set joseHeader [CkJwt_getHeader $jwt $accessToken]

puts "$joseHeader"
# The joseHeader contains this:   {"kid":"anSaRDPfWGOSCVNZEIZB9quCbNsdsvl5uWGBzxbudWQ","alg":"RS256"}

set json [new_CkJsonObject]

CkJsonObject_Load $json $joseHeader
set kid [CkJsonObject_stringOf $json "kid"]
puts "kid to find: $kid"

# ------------------------
# Step 2: Find the key with the same "kid" in the Okta web keys.

set sbKid [new_CkStringBuilder]

set e ""
set n ""

set i 0
set count_i [CkJsonObject_SizeOfArray $jsonWebKeys "keys"]
set bFound 0
set iMatch 0
while {expr [$bFound == 0]  &&  [$i < $count_i]} {
    CkJsonObject_put_I $jsonWebKeys $i
    CkStringBuilder_Clear $sbKid
    CkJsonObject_StringOfSb $jsonWebKeys "keys[i].kid" $sbKid
    puts "checking kid: [CkStringBuilder_getAsString $sbKid]"

    if {[CkStringBuilder_ContentsEqual $sbKid $kid 1] == 1} then {
        set e [CkJsonObject_stringOf $jsonWebKeys "keys[i].e"]
        set n [CkJsonObject_stringOf $jsonWebKeys "keys[i].n"]
        # Exit the loop. 
        puts "Found matching kid."
        set iMatch $i
        set bFound 1
    }

    set i [expr $i + 1]
}

if {$bFound == 0} then {
    puts "No matching key ID found."
    delete_CkJsonObject $jsonToken
    delete_CkJsonObject $jsonWebKeys
    delete_CkJwt $jwt
    delete_CkJsonObject $json
    delete_CkStringBuilder $sbKid
    exit
}

puts "Matching key:"
puts "  exponent = $e"
puts "  modulus = $n"

# ------------------------
# Step 3: Load the RSA modulus and exponent into a Chilkat public key object.
set pubkey [new_CkPublicKey]

# Get the matching JSON key from the array of keys.
CkJsonObject_put_I $jsonWebKeys $iMatch
# jsonWebKey is a CkJsonObject
set jsonWebKey [CkJsonObject_ObjectOf $jsonWebKeys "keys[i]"]
set success [CkPublicKey_LoadFromString $pubkey [CkJsonObject_emit $jsonWebKey]]
if {$success == 0} then {
    puts "Failed to load JSON web key."
    puts [CkJsonObject_emit $jsonWebKey]
    puts [CkPublicKey_lastErrorText $pubkey]
    delete_CkJsonObject $jsonWebKey

    delete_CkJsonObject $jsonToken
    delete_CkJsonObject $jsonWebKeys
    delete_CkJwt $jwt
    delete_CkJsonObject $json
    delete_CkStringBuilder $sbKid
    delete_CkPublicKey $pubkey
    exit
}

delete_CkJsonObject $jsonWebKey

puts "successfully loaded web key."

# OK.. we have the desired JSON web key loaded into our public key object.
# Now we can verify the access token.

# ------------------------
# Step 4: Verify the access token.
set bVerified [CkJwt_VerifyJwtPk $jwt $accessToken $pubkey]
if {$bVerified == 1} then {
    puts "The access token is valid."
} else {
    puts "The access token is NOT valid."
}


delete_CkJsonObject $jsonToken
delete_CkJsonObject $jsonWebKeys
delete_CkJwt $jwt
delete_CkJsonObject $json
delete_CkStringBuilder $sbKid
delete_CkPublicKey $pubkey