How solve Curl error 60, SSL certificate issue?

Sometimes, we use curl. But, there is a error like under.

$ curl -L | bash

curl: (60) SSL certificate problem: self signed certificate
More details here:

curl failed to verify the legitimacy of the server and therefore could not establish a secure connection to it. To learn more about this situation and how to fix it, please visit the web page mentioned above.

How can we fix it? If you appened -k option, you can download normally.

$ curl -L -k | bash

And here is another solution stackoverflow _ curl: (60) SSL certificate problem: unable to get local issuer certificate.