SOLVED: the problem was with the certificate chain (it was a subdomain). The sysadmin had to re-sign the certs.
Anyone has faced it? I’m running out of ideas, Google can’t help me either 
- this endpoint is used by other Python applications with no problem:
I20151117-16:28:55.815(-2)? Exception while invoking method 'getRandomLetter' Error: CERT_UNTRUSTED
I20151117-16:28:55.815(-2)? at Object.Future.wait (/Users/gabrielpugliese/.meteor/packages/meteor-tool/.1.1.10.1b51q9m++os.osx.x86_64+web.browser+web.cordova/mt-os.osx.x86_64/dev_bundle/server-lib/node_modules/fibers/future.js:398:15)
I20151117-16:28:55.815(-2)? at Object.<anonymous> (packages/meteor/helpers.js:119:1)
I20151117-16:28:55.815(-2)? at Object.HTTP.call (packages/meteorhacks_kadira/lib/hijack/http.js:10:1)
I20151117-16:28:55.816(-2)? at Object.HTTP.get (packages/http/httpcall_common.js:50:1)
I20151117-16:28:55.816(-2)? at [object Object].getRandomLetter (webpack:///Users/gabrielpugliese/Workspace/XXXXX/modules/Letter/server/methods.js:8:19)
I20151117-16:28:55.816(-2)? at [object Object].methodMap.(anonymous function) (packages/meteorhacks_kadira/lib/hijack/wrap_session.js:164:1)
I20151117-16:28:55.817(-2)? at maybeAuditArgumentChecks (livedata_server.js:1698:12)
I20151117-16:28:55.817(-2)? at livedata_server.js:708:19
I20151117-16:28:55.817(-2)? at [object Object]._.extend.withValue (packages/meteor/dynamics_nodejs.js:56:1)
I20151117-16:28:55.817(-2)? at livedata_server.js:706:40
I20151117-16:28:55.817(-2)? - - - - -
I20151117-16:28:55.817(-2)? at SecurePair.<anonymous> (tls.js:1381:32)
I20151117-16:28:55.818(-2)? at SecurePair.emit (events.js:92:17)
I20151117-16:28:55.818(-2)? at SecurePair.maybeInitFinished (tls.js:980:10)
I20151117-16:28:55.818(-2)? at CleartextStream.read [as _read] (tls.js:472:13)
I20151117-16:28:55.818(-2)? at CleartextStream.Readable.read (_stream_readable.js:341:10)
I20151117-16:28:55.818(-2)? at EncryptedStream.write [as _write] (tls.js:369:25)
I20151117-16:28:55.819(-2)? at doWrite (_stream_writable.js:226:10)
I20151117-16:28:55.819(-2)? at writeOrBuffer (_stream_writable.js:216:5)
I20151117-16:28:55.819(-2)? at EncryptedStream.Writable.write (_stream_writable.js:183:11)
I20151117-16:28:55.819(-2)? at write (_stream_readable.js:602:24)
I20151117-16:28:55.820(-2)? at flow (_stream_readable.js:611:7)
I20151117-16:28:55.820(-2)? at Socket.pipeOnReadable (_stream_readable.js:643:5)