Discovery is the process of asking the server for its configuration.

You send the discovery HTTP request to the URL the user has
configured.  If the user hasn't specified a path, use "/".

Then make a GET request to that URL with either Accept header set to
"text/x-camli-configuration" or the the URL query parameter
"camli.mode" set to "config":

   GET /some/user/?camli.mode=config HTTP/1.1
   Host: camlihost.example.com

Or:

   GET / HTTP1.1
   Host: 127.0.0.1
   Accept: text/x-camli-configuration

The response is a JSON document:

{
  "blobRoot": "/bs-and-maybe-also-index/",
  "directoryHelper": "/ui/tree/",
  "downloadHelper": "/ui/download/",
  "jsonSignRoot": "/sighelper/",
  "ownerName": "The User Name",
  "publishRoots": {},
  "searchRoot": "/my-search/",
  "signing": {
    "publicKey": "/sighelper/camli/sha1-f72d9090b61b70ee6501cceacc9d81a0801d32f6",
    "publicKeyBlobRef": "sha1-f72d9090b61b70ee6501cceacc9d81a0801d32f6",
    "publicKeyId": "94DE83C46401800C",
    "signHandler": "/sighelper/camli/sig/sign",
    "verifyHandler": "/sighelper/camli/sig/verify"
  },
  "statusRoot": "/status/",
  "storageGeneration": "231ceff7a04a77cdf881b0422ea733334eee3b8f",
  "storageInitTime": "2012-11-30T03:34:47Z",
  "syncHandlers": [
    {
      "from": "/bs/",
      "to": "/index-mysql/",
      "toIndex": true
    },
    {
      "from": "/bs/",
      "to": "/sto-s3/",
      "toIndex": false
    }
  ],
  "thumbVersion": "2",
  "uiRoot": "/ui/",
  "uploadHelper": "/ui/?camli.mode=uploadhelper",
  "wsAuthToken": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
}

TODO: document these more