(Tcl) OAuth2 Token using IdentityServer4 with Client Credentials

Demonstrates how to get an OAuth2 access token using the client credential flow with IdentityServer4.

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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.

set http [new_CkHttp]

# The first step is to fetch your IdentityServer4's discovery document
# (OpenID Connect defines a discovery mechanism, called OpenID Connect Discovery, where an OpenID server publishes its metadata at a well-known URL, 
# typically https://server.com/.well-known/openid-configuration

# resp is a CkHttpResponse
set resp [CkHttp_QuickRequest $http "GET" "https://localhost:5000/.well-known/openid-configuration"]
if {[CkHttp_get_LastMethodSuccess $http] != 1} then {
    puts [CkHttp_lastErrorText $http]
    delete_CkHttp $http
    exit
}

if {[CkHttpResponse_get_StatusCode $resp] != 200} then {
    puts "Received response status code [CkHttpResponse_get_StatusCode $resp]"
    puts "Response body containing error text or JSON:"
    puts [CkHttpResponse_bodyStr $resp]
    delete_CkHttpResponse $resp

    delete_CkHttp $http
    exit
}

set json [new_CkJsonObject]

set success [CkJsonObject_Load $json [CkHttpResponse_bodyStr $resp]]
delete_CkHttpResponse $resp

# We have the discovery document, which contains something like this:

# You can use this online tool to generate parsing code from sample JSON: 
# Generate Parsing Code from JSON

# {
#   "issuer": "https://localhost:5000",
#   "jwks_uri": "https://localhost:5000/.well-known/openid-configuration/jwks",
#   "authorization_endpoint": "https://localhost:5000/connect/authorize",
#   "token_endpoint": "https://localhost:5000/connect/token",
#   "userinfo_endpoint": "https://localhost:5000/connect/userinfo",
#   "end_session_endpoint": "https://localhost:5000/connect/endsession",
#   "check_session_iframe": "https://localhost:5000/connect/checksession",
#   "revocation_endpoint": "https://localhost:5000/connect/revocation",
#   "introspection_endpoint": "https://localhost:5000/connect/introspect",
#   "frontchannel_logout_supported": true,
#   "frontchannel_logout_session_supported": true,
#   "backchannel_logout_supported": true,
#   "backchannel_logout_session_supported": true,
#   "scopes_supported": [
#     "openid",
#     "profile",
#     "email",
#     "MyCompany.profile",
#     "MyCompany.Identity.WebApi",
#     "MyCompany.TriHub.WebApi",
#     "offline_access"
#   ],
#   "claims_supported": [
#     "sub",
#     "updated_at",
#     "locale",
#     "zoneinfo",
#     "birthdate",
#     "gender",
#     "website",
#     "profile",
#     "preferred_username",
#     "nickname",
#     "middle_name",
#     "given_name",
#     "family_name",
#     "name",
#     "picture",
#     "email_verified",
#     "email",
#     "userId",
#     "groups",
#     "fullname"
#   ],
#   "grant_types_supported": [
#     "authorization_code",
#     "client_credentials",
#     "refresh_token",
#     "implicit",
#     "password"
#   ],
#   "response_types_supported": [
#     "code",
#     "token",
#     "id_token",
#     "id_token token",
#     "code id_token",
#     "code token",
#     "code id_token token"
#   ],
#   "response_modes_supported": [
#     "form_post",
#     "query",
#     "fragment"
#   ],
#   "token_endpoint_auth_methods_supported": [
#     "client_secret_basic",
#     "client_secret_post"
#   ],
#   "subject_types_supported": [
#     "public"
#   ],
#   "id_token_signing_alg_values_supported": [
#     "RS256"
#   ],
#   "code_challenge_methods_supported": [
#     "plain",
#     "S256"
#   ]
# }
# 

# The next steps are to (1) get the token_endpoint,
# and (2) verify that the client_credentials grant type is supported.

set tokenEndpoint [CkJsonObject_stringOf $json "token_endpoint"]

# grantTypes is a CkJsonArray
set grantTypes [CkJsonObject_ArrayOf $json "grant_types_supported"]
set clientCredentialsIdx [CkJsonArray_FindString $grantTypes "client_credentials" 1]
delete_CkJsonArray $grantTypes

# If clientCredentialsIdx is less then zero (-1) then the "client_credentials" string was not found.
if {$clientCredentialsIdx < 0} then {
    puts "The client credentials grant type is not supported."
    delete_CkHttp $http
    delete_CkJsonObject $json
    exit
}

# Request the access token using our Client ID and Client Secret.
# We're going to duplicate this CURL statement:

# curl --request POST \
#   --url '<tokenEndpoint>' \
#   --header 'content-type: application/x-www-form-urlencoded' \
#   --data 'grant_type=client_credentials&client_id=CLIENT_ID&client_secret=CLIENT_SECRET'

set req [new_CkHttpRequest]

CkHttpRequest_put_HttpVerb $req "POST"
CkHttpRequest_AddParam $req "grant_type" "client_credentials"
CkHttpRequest_AddParam $req "client_id" "CLIENT_ID"
CkHttpRequest_AddParam $req "client_secret" "CLIENT_SECRET"

set resp [CkHttp_PostUrlEncoded $http $tokenEndpoint $req]
if {[CkHttp_get_LastMethodSuccess $http] == 0} then {
    puts [CkHttp_lastErrorText $http]
    delete_CkHttp $http
    delete_CkJsonObject $json
    delete_CkHttpRequest $req
    exit
}

# Make sure we got a 200 response status code, otherwise it's an error.
if {[CkHttpResponse_get_StatusCode $resp] != 200} then {
    puts "POST to token endpoint failed."
    puts "Received response status code [CkHttpResponse_get_StatusCode $resp]"
    puts "Response body containing error text or JSON:"
    puts [CkHttpResponse_bodyStr $resp]
    delete_CkHttpResponse $resp

    delete_CkHttp $http
    delete_CkJsonObject $json
    delete_CkHttpRequest $req
    exit
}

set success [CkJsonObject_Load $json [CkHttpResponse_bodyStr $resp]]
delete_CkHttpResponse $resp

# Our JSON response should contain this:
# {
#   "access_token":"eyJz93a...k4laUWw",
#   "token_type":"Bearer",
#   "expires_in":86400
# }

# Get the access token:
set accessToken [CkJsonObject_stringOf $json "access_token"]

# The access token is what gets added to "Authorization: Bearer <access_token>"
# for the subsequent REST API calls..

delete_CkHttp $http
delete_CkJsonObject $json
delete_CkHttpRequest $req