(WIP) Okta token auth for Process Automation 5.1.0

[gschueler]

No description provided.

[ahormazabal]

This looks great as a first step. The change i'd propose is that the actual token api call is OAuth standard, so there's no need to tie it to Okta. Instead we could have a command rd oauth token or something alike.
The flow to implement is called client credentials, although there are more that we could implement in the future (the device grant is very interesting, its the one used to configure netflix on TV).

Examples of token retrieval calls:

Azure:

### Authorization by token, AZURE
POST https://login.microsoftonline.com/ba468bd4-88e0-40fc-8115-5478ce6e8eb6/oauth2/v2.0/token
Content-Type: application/x-www-form-urlencoded
Accept: application/json

grant_type=client_credentials &
client_id=azure_client_id &
client_secret=azure_client_secret &
scope=api://rd-api-oauth/.default &
state=myownpersonalstate123

# Response
{
  "token_type": "Bearer",
  "expires_in": 3599,
  "ext_expires_in": 3599,
  "access_token": "eyJ0eXAiOiJKV1QiLC..."
}

Ping:

### Authorization by token, Ping
POST https://auth.pingone.com/8e142195-3912-4340-85da-c41c069e66f0/as/token
Content-Type: application/x-www-form-urlencoded
Accept: application/json

grant_type=client_credentials &
client_id=ping_client_id &
client_secret=ping_client_secret &
scope=rundeck.api.admin.access &
state=myownpersonalstate123

#Response
{
  "access_token": "eyJraWQiOiJmZDZjNzBl...",
  "token_type": "Bearer",
  "expires_in": 3600,
  "scope": "rundeck.api.admin.access"
}

Okta

### Authorization by token, Okta
POST https://trial-1510695.okta.com/oauth2/default/v1/token
Content-Type: application/x-www-form-urlencoded
Accept: application/json

grant_type=client_credentials &
client_id=okta_client_id &
client_secret=okta_client_secret &
scope=rd.okta.api.admin.access &
state=myownpersonalstate123

#Response
{
  "token_type": "Bearer",
  "expires_in": 3600,
  "access_token": "eyJraWQiOiJqaDJWYk...",
  "scope": "rd.okta.api.admin.access"
}