SSL certificate cannot be verified for some websites

[quyin]

when downloading from some websites, curl gives this error. example: http://api.ecologylab.net/DownloaderPool/page/download.json?url=https://twitter.com/ajitjain85

explanation: http://curl.haxx.se/docs/sslcerts.html

different strategies:

1. update CA bundle on the downloader machine, which requires root privilege;
2. bypass SSL certificate verification.

needs further discussion.