Service Broker locked in state `SYNCHRONIZING` after erroneous request

[svkrieger]

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Issue

Sending a broker update including empty strings for username and password will cause the broker to be locked in state SYNCHRONIZING.

Context

When updating a service broker with empty strings for username or password like so:

$ cf curl -X PATCH "/v3/service_brokers/08f7ad8a-aee8-4211-b605-3b4c88a874b1" -d '{"authentication": {"type":"basic", "credentials":{"username":"", "password":""}}}'

the async job will fail with a 500 - unknown error:

$ cf curl "/v3/jobs/8c88693f-0958-4ff1-ae5f-979b00ee8198"
{
  "guid": "8c88693f-0958-4ff1-ae5f-979b00ee8198",
  "created_at": "2022-08-22T08:55:07Z",
  "updated_at": "2022-08-22T08:55:07Z",
  "operation": "service_broker.update",
  "state": "FAILED",
  "errors": [
    {
      "title": "UnknownError",
      "detail": "An unknown error occurred.",
      "code": 10001
    }
  ],
  "warnings": [],
  "links": {
    "self": {
      "href": "https://api.cf.dev22.aws.bndl.sapcloud.io/v3/jobs/8c88693f-0958-4ff1-ae5f-979b00ee8198"
    },
    "service_brokers": {
      "href": "https://api.cf.dev22.aws.bndl.sapcloud.io/v3/service_brokers/08f7ad8a-aee8-4211-b605-3b4c88a874b1"
    }
  }
}

The service broker stays in state SYNCHRONIZING:

-[ RECORD 2 ]---------+-------------------------------------------------------
id                    | 2
guid                  | 08f7ad8a-aee8-4211-b605-3b4c88a874b1
created_at            | 2022-08-22 08:42:36.700996
updated_at            | 2022-08-22 08:55:07.550528
name                  | ta-sb
broker_url            | https://at-sb.cfapps.dev22.aws.bndl.sapcloud.io
auth_password         | PLbOfqnbHa/Cb/zmAegTHg==
salt                  | f88f636820c17ac2
auth_username         | admin
space_id              |
encryption_key_label  | encryption_key_0
encryption_iterations | 2048
state                 | SYNCHRONIZING

And updating the broker with the correct credentials (actually updating the broker with anything else than metadata) is not possible from then on:

$ cf curl -X PATCH "/v3/service_brokers/08f7ad8a-aee8-4211-b605-3b4c88a874b1" -d '{"authentication": {"type":"basic", "credentials":{"username":"admin", "password":"admin"}}}'
{
  "errors": [
    {
      "detail": "Cannot update a broker when other operation is already in progress",
      "title": "CF-UnprocessableEntity",
      "code": 10008
    }
  ]
}

Steps to Reproduce

see above

Expected result

The broker does not get locked by a erroneous request.

Current result

The broker is locked and no interactions with the broker are possible anymore.

Possible Fix

The CC should either reject a request which includes empty strings for username or password. This is probably the best solution, as we don't need to enqueue a job.

Another solution would be to set the broker state to SYNCHRONIZATION_FAILED and return an appropriate error message to the client if the sequel validations fail.