AT:

• there is an api endpoint providing process definitions grouped by key, version & available tenants

  [
  // a shared process definition (no tenant specified on the definition itself)
    {
      "key": "abc",
      "name": "ABC",
      "versions": [
        {
          "version": "ALL",
  // the version "ALL" contains the merged tenant list of all versions 
          "tenants": [
            {
              "id": null,
              "name": "Not defined"
            },
            {
              "id": "tenant1",
              "name": "Tenant 1"
            },
            {
              "id": "tenant2",
              "name": "Tenant 2"
            }
          ]
        },
        {
          "version": "1",
  // for shared process definitions all available tenants + the 'None' tenant are available
          "tenants": [
            {
              "id": null,
              "name": "Not defined"
            },
            {
              "id": "tenant1",
              "name": "Tenant 1"
            },
            {
              "id": "tenant2",
              "name": "Tenant 2"
            }
          ]
        }
      ]
    },
  // tenant specific process definition
    {
      "key": "xyz",
      "name": "XYZ",
      "versions": [
  // the version "ALL" contains the merged tenant list of all versions 
        {
          "version": "ALL",
          "tenants": [
            {
              "id": "tenant1",
              "name": "Tenant 1"
            },
            {
              "id": "tenant2",
              "name": "Tenant 2"
            }
          ]
        },
  // version 2 only available for tenant2
        {
          "version": "2",
          "tenants": [
            {
              "id": "tenant2",
              "name": "Tenant 2"
            }
          ]
        },
  // version 1 available for tenant1 & tenant2 
        {
          "version": "1",
          "tenants": [
            {
              "id": "tenant1",
              "name": "Tenant 1"
            },
            {
              "id": "tenant2",
              "name": "Tenant 2"
            }
          ]
        }
      ]
    },
  ]
  

• the process/decision definition xml endpoint is extended with a tenantId query parameter to get tenant specific definition xml's, e.g.:
  /api/process-definition/xml?processDefinitionKey=Document_Check_Handling&processDefinitionVersion=7&tenantId=tenant1