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

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

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load ./chilkat.dll

# 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:

set http [new_CkHttp]

set sbJsonKeys [new_CkStringBuilder]

set success [CkHttp_QuickGetSb $http "https://cognito-idp.us-east-2.amazonaws.com/us-east-2_******/.well-known/jwks.json" $sbJsonKeys]
if {$success == 0} then {
    puts [CkHttp_lastErrorText $http]
    delete_CkHttp $http
    delete_CkStringBuilder $sbJsonKeys
    exit
}

set jsonKeys [new_CkJsonObject]

CkJsonObject_LoadSb $jsonKeys $sbJsonKeys
CkJsonObject_put_EmitCompact $jsonKeys 0
puts [CkJsonObject_emit $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 is a CkJsonObject
set jsonKey1 [CkJsonObject_ObjectOf $jsonKeys "keys[0]"]
if {[CkJsonObject_get_LastMethodSuccess $jsonKeys] == 0} then {
    puts "Did not get the 1st JSON public key."
    delete_CkHttp $http
    delete_CkStringBuilder $sbJsonKeys
    delete_CkJsonObject $jsonKeys
    exit
}

set pubKey1 [new_CkPublicKey]

set success [CkPublicKey_LoadFromString $pubKey1 [CkJsonObject_emit $jsonKey1]]
if {$success == 0} then {
    puts [CkPublicKey_lastErrorText $pubKey1]
    delete_CkHttp $http
    delete_CkStringBuilder $sbJsonKeys
    delete_CkJsonObject $jsonKeys
    delete_CkPublicKey $pubKey1
    exit
}

delete_CkJsonObject $jsonKey1

puts "Success"

set jwt [new_CkJwt]

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

# First verify the signature.
set sigVerified [CkJwt_VerifyJwtPk $jwt $token $pubKey1]
puts "verified: $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.
set leeway 60
set bTimeValid [CkJwt_IsTimeValid $jwt $token $leeway]
puts "time constraints valid: $bTimeValid"

# Now let's recover the original claims JSON (the payload).
set payload [CkJwt_getPayload $jwt $token]
# The payload will likely be in compact form:
puts "$payload"

# We can format for human viewing by loading it into Chilkat's JSON object
# and emit.
set json [new_CkJsonObject]

set success [CkJsonObject_Load $json $payload]
CkJsonObject_put_EmitCompact $json 0
puts [CkJsonObject_emit $json]

# We can recover the original JOSE header in the same way:
set joseHeader [CkJwt_getHeader $jwt $token]
# The payload will likely be in compact form:
puts "$joseHeader"

# We can format for human viewing by loading it into Chilkat's JSON object
# and emit.
set success [CkJsonObject_Load $json $joseHeader]
CkJsonObject_put_EmitCompact $json 0
puts [CkJsonObject_emit $json]

delete_CkHttp $http
delete_CkStringBuilder $sbJsonKeys
delete_CkJsonObject $jsonKeys
delete_CkPublicKey $pubKey1
delete_CkJwt $jwt
delete_CkJsonObject $json