Source Mailchimp: support oauth

[sherifnada]

Tell us about the problem you're trying to solve

With the release of Airbyte Cloud, we need to start supporting Oauth for this connector, since it's the recommended way of authenticating users into a SaaS application.

If this connector doesn't support oauth already (i.e: doesn't accept a client_id and client_secret) then we need to update its spec to accept those parameters. There are two ways to do this:

If the connector already supports some auth mechanism like api_key, I suggest that this be a oneof nested inside a top-level field called "authentication":

{ authentication: { type: object oneOf: [ // api key, // oauth ] } }

If the connector only supports webflow oauth, then no changes are needed to the properties format and we will only need to add annotations.

See the connector spec reference in the docs for reference on how a oneof can be implemented.

This should be done in a backwards compatible manner i.e: users currently supplying authentication info in the config's top-level should not be impacted by this change.

Acceptance Criteria

1. The connector supports oauth webflow authentication with client_id/client_secret in a backwards compatible manner
2. Oauth properties are annotated properly. See this PR for an example

• Source Mailchimp: add oauth flow (java part) #7406

[igrankova]

OAuth Application is registered:
https://us2.admin.mailchimp.com/account/oauth2/client?id=347762220844

https://mailchimp.com/developer/marketing/guides/access-user-data-oauth-2/

Oath QA authorization flow passed

[antixar]

Source Mailchimp: add oauth flow (java part)

https://mailchimp.com/developer/marketing/guides/access-user-data-oauth-2/

=========== JAVA PART ================

Approve access from the customer side using:
client_id

https://login.mailchimp.com/oauth2/authorize?response_type=code&client_id=1234567890&redirect_uri=https://airbyte.io/

Get redirect url with 'code':

https://airbyte.io/?code=33333333

Obtain token using

curl https://login.mailchimp.com/oauth2/token
-X POST
-H 'Content-Type: application/json'
-d '{
"client_id": "1234567890",
"client_secret": "2222222",
"grant_type": "authorization_code",
"code": "3333333",
"redirect_uri": "https://airbyte.io/"
}'

RESPONSE:
{
"access_token": "1q2w3e4r5t6y.",
"expires_in": "0",
"scope": null
}

OAuth access tokens do not expire.

Obtain server_prefix (dc) using

curl https://login.mailchimp.com/oauth2/metadata
-X GET
-H 'Authorization: Bearer <access_token>'

RESPONSE:
{
"dc": "us2",
"role": "admin",
"accountname": "Airbyte",
"user_id": 123,
"login": {
"email": "email@email.com",
"avatar": null,
"login_id": 12345,
"login_name": "email@email.com",
"login_email": "email@email.com"
},
"login_url": "https://login.mailchimp.com",
"api_endpoint": "https://us2.api.mailchimp.com"
}

============== PYTHON PART =====================

API requests using access_token and server_prefix (dc).

$ curl
-s https://{server_prefix}.api.mailchimp.com/3.0/campaigns
-H 'Authorization: Bearer <access_token>'

[annalvova05]

Can not test OAuth flow locally, due to impossible set localhost as redirect URL in Mailchimp. Move to ON Hold