How to get the groups associated to organizations using JSON Web Services

Issue

There is no method available in the JSON Web Services API to obtain the groups (i.e. sites) associated to organizations. Is there a way to get them?

Environment

Liferay DXP 7.0, 7.1, 7.2, 7.3

Resolution

There are two auxiliary methods available in the JSON WS API than can be combined to get the desired result:
- /organization/get-organizations:
  - Input: companyId, parentOrganizationId
  - Output: [Organization]
- /group/get-organizations-groups
  - Input: [Organization]
  - Output: [Group]
The complex objects Organization and Group are represented as JSON objects.
These two methods are composable: the output of /organization/get-organizations can be used, without modification, as the input of /group/get-organizations-groups.

An example:

The first method /organization/get-organizations can be called with the command:
```
curl http://localhost:8080/api/jsonws/organization/get-organizations \
  -u test@liferay.com:test \
  -d companyId=20101 \
  -d parentOrganizationId=0
```
where we have chosen a particular Liferay instance with companyId=20101, and no restriction on the organizations with parentOrganizationId=0.

The output is a JSON list:

[
  {
    [...], "companyId": "20101", [...], "organizationId": "41003", "parentOrganizationId": "0", [...]
  },
  {
    [...], "companyId": "20101", [...], "organizationId": "41008", "parentOrganizationId": "0", [...]
  }
]

This output can be escaped and used as input in the second method /group/get-organizations-groups:

curl http://localhost:9090/api/jsonws/group/get-organizations-groups \
  -u test@liferay.com:test \
  -d organizations=%5B%0A%20%20%7B%0A%20%20%20%20%22comments%22[...]%20%7D%0A%5D

The output is another JSON list with the desired groups:

[
  {
    [...], "groupId": "41005", "groupKey": "org01 LFR_ORGANIZATION", [...]
  },
  {
    [...], "groupId": "41010", "groupKey": "org02 LFR_ORGANIZATION", [...]
  }
]