Session pojo and serialization

{
  "capabilities": {
     "urn:ietf:params:jmap:core":
       "maxSizeUpload": 10000000,
       "maxConcurrentUpload": 4,
       "maxSizeRequest": 10000000,
       "maxConcurrentRequests": 4,
       "maxCallsInRequest": 16,
       "maxObjectsInGet": 500,
       "maxObjectsInSet": 500,
       "collationAlgorithms": ["i;unicode-casemap"]
     },
     "urn:ietf:params:jmap:mail":
       "maxMailboxesPerEmail": 10000000,
       "maxMailboxDepth": null,
       "maxSizeMailboxName": 200,
       "maxSizeAttachmentsPerEmail": 20000000,
       "mayCreateTopLevelMailbox": true,
       "emailQuerySortOptions": ["receivedAt", "cc", "from", "to", "subject", "size", "sentAt", "hasKeyword", "uid", "Id"],
     },
  },
  "accounts": [
      "bob@apache.org" : {
        "name": "bob@apache.org",
        "isPersonal": "true",
        "isReadOnly": "false",
        "capabilities": {...},
      }
  ],
  "primaryAccounts": {
     "urn:ietf:params:jmap:mail": "bob@apache.org"
  },
  "username": "bob@apache.org",
  "apiUrl": "https://example.com/jmap/api",
  "downloadUrl": "https://example.com/jmap/download/{accountId}/{blobId}/{name}?accept={type}",
  "uploadUrl": "https://example.com/jmap/upload/{accountId}",
  "eventSourceUrl": "https://example.com/jmap/eventsource/?types={types}&closeafter={closeafter}&ping={ping}",
  "state": null
}