$ nix-build --expr '(import ./. {}).fetchurl { url = "https://example.com"; hash = ""; }'
this derivation will be built:
  /nix/store/ryngk5xndc9sdhpw1pk5g8bi7b7dix8a-example.com.drv
building '/nix/store/ryngk5xndc9sdhpw1pk5g8bi7b7dix8a-example.com.drv'...
structuredAttrs is enabled

trying https://example.com
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0   0     0   0     0     0     0  --:--:-- --:--:-- --:--:--     0
curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
More details here: https://curl.se/docs/sslcerts.html

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 webpage mentioned above.
Warning: Problem (retrying all errors). Will retry in 1 second. 3 retries left.
  0     0   0     0   0     0     0     0  --:--:-- --:--:-- --:--:--     0
curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
More details here: https://curl.se/docs/sslcerts.html

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 webpage mentioned above.
Warning: Problem (retrying all errors). Will retry in 2 seconds. 2 retries
Warning: left.
  0     0   0     0   0     0     0     0  --:--:-- --:--:-- --:--:--     0
curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
More details here: https://curl.se/docs/sslcerts.html

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 webpage mentioned above.
Warning: Problem (retrying all errors). Will retry in 4 seconds. 1 retry left.
  0     0   0     0   0     0     0     0  --:--:-- --:--:-- --:--:--     0
curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
More details here: https://curl.se/docs/sslcerts.html

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 webpage mentioned above.
error checking the existence of https://tarballs.nixos.org//sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=:
curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
More details here: https://curl.se/docs/sslcerts.html

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 webpage mentioned above.
error: cannot download example.com from any mirror
error: Cannot build '/nix/store/ryngk5xndc9sdhpw1pk5g8bi7b7dix8a-example.com.drv'.
       Reason: builder failed with exit code 1.
       Output paths:
         /nix/store/6jix8ihxjjw4l9l2lpjvjr4wv9psmp7j-example.com
       Last 25 log lines:
       > Warning: Problem (retrying all errors). Will retry in 2 seconds. 2 retries
       > Warning: left.
       >   0     0   0     0   0     0     0     0  --:--:-- --:--:-- --:--:--     0
       > curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
       > More details here: https://curl.se/docs/sslcerts.html
       >
       > 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 webpage mentioned above.
       > Warning: Problem (retrying all errors). Will retry in 4 seconds. 1 retry left.
       >   0     0   0     0   0     0     0     0  --:--:-- --:--:-- --:--:--     0
       > curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
       > More details here: https://curl.se/docs/sslcerts.html
       >
       > 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 webpage mentioned above.
       > error checking the existence of https://tarballs.nixos.org//sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=:
       > curl: (60) SSL certificate OpenSSL verify result: unable to get local issuer certificate (20)
       > More details here: https://curl.se/docs/sslcerts.html
       >
       > 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 webpage mentioned above.
       > error: cannot download example.com from any mirror
       For full logs, run:
         nix log /nix/store/ryngk5xndc9sdhpw1pk5g8bi7b7dix8a-example.com.drv

$ nix-build --expr '(import ./. {}).fetchurl { url = "https://example.com"; hash = ""; }'
this derivation will be built:
  /nix/store/53h6qx0bkr1vwxc2b2l535xyxhl8vvsg-example.com.drv
building '/nix/store/53h6qx0bkr1vwxc2b2l535xyxhl8vvsg-example.com.drv'...
structuredAttrs is enabled

trying https://example.com
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   513 100   513   0     0  1708     0  --:--:-- --:--:-- --:--:--  1710
error: hash mismatch in fixed-output derivation '/nix/store/53h6qx0bkr1vwxc2b2l535xyxhl8vvsg-example.com.drv':
         specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
            got:    sha256-b1Y1A182rVALT8S7eBa7cu9VlOG8rkT6B0xemI/EwP4=