polettix/taskwarrior-letsencrypt.md

## taskwarrior-letsencrypt.md

      
    Raw
  

              taskwarrior-letsencrypt.md
            
          
    When you set Let's Encrypt up, you will:

generate a key on your computer (among other things), which we will call domain.key
regularly update a certificate file via Let's Encrypt (most probably using one of the
Acme Client Implementations), we will
call this file domain.crt

The domain.key file is for your eyes only; you should keep it safe where you run taskd
and set server.key to point to it.
The domain.crt file actually contains two certificates: one is for your domain, signed
by Let's Encrypt; the other one is a CA intermediate file that tells the world Let's
Encrypt is entitled to sign certificates, and it is signed by a "major" CA whose certificate
is widespread across browsers/libraries.
For example, this is what I get for polettix.it (I removed some lines inside the certificate):
-----BEGIN CERTIFICATE-----
MIIGNTCCBR2gAwIBAgISAyzjWXqpc+XbdY5msxk1ePBhMA0GCSqGSIb3DQEBCwUA
MEoxCzAJBgNVBAYTAlVTMRYwFAYDVQQKEw1MZXQncyBFbmNyeXB0MSMwIQYDVQQD
ExpMZXQncyBFbmNyeXB0IEF1dGhvcml0eSBYMzAeFw0xNjA4MTUyMjEwMDBaFw0x
NjExMTMyMjEwMDBaMBYxFDASBgNVBAMTC3BvbGV0dGl4Lml0MIICIjANBgkqhkiG
9w0BAQEFAAOCAg8AMIICCgKCAgEAusStlvvKLfyyArC7Qs3j7Bis8JSuPS8gGqm8
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b24gYnkgUmVseWluZyBQYXJ0aWVzIGFuZCBvbmx5IGluIGFjY29yZGFuY2Ugd2l0
aCB0aGUgQ2VydGlmaWNhdGUgUG9saWN5IGZvdW5kIGF0IGh0dHBzOi8vbGV0c2Vu
Y3J5cHQub3JnL3JlcG9zaXRvcnkvMA0GCSqGSIb3DQEBCwUAA4IBAQAA3jUihVI9
MfTZJEePQBvCUMjrGP1/ikfWUE2iKVVSzeu5bEs1NFW00HVTQXMKNR7LNiI0j9zD
HIkMvNG9ltamAjY9+NdGN98rlMveuZxx8quPYsQ8U6W2cTUna6DxMNTVnIvi4rRV
TgOWru2wG7n+U9BjeOT/7p+MzI+TPb/N2TMNua7XFn/vmp/qL7NAMFQ7R1C9CTOQ
l/ACM5i3e5MshSn8pg9EQNYDsr5MoUySLZtkJIegIP1zvNU9Yl0nvNoa+f4c97C0
AUD5pOlsXXuFidxtdN6ey7iA+SgLE+ZEZWfC9x1szEx6qlY0ErIi0ywE/lWOTGfO
Dhyov1fiSseU
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
MIIEkjCCA3qgAwIBAgIQCgFBQgAAAVOFc2oLheynCDANBgkqhkiG9w0BAQsFADA/
MSQwIgYDVQQKExtEaWdpdGFsIFNpZ25hdHVyZSBUcnVzdCBDby4xFzAVBgNVBAMT
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wApIvJSwtmVi4MFU5aMqrSDE6ea73Mj2tcMyo5jMd6jmeWUHK8so/joWUoHOUgwu
X4Po1QYz+3dszkDqMp4fklxBwXRsW10KXzPMTZ+sOPAveyxindmjkW8lGy+QsRlG
PfZ+G6Z6h7mjem0Y+iWlkYcV4PIWL1iwBi8saCbGS5jN2p8M+X+Q7UNKEkROb3N6
KOqkqm57TH2H3eDJAkSnh6/DNFu0Qg==
-----END CERTIFICATE-----

On the server side, you can just point server.cert to point to where
domain.crt is located.
On the client side, you have to take the second certificate from the
file, save in a file of its own (e.g. letsencrypt-ca.crt) and configure
it as taskd.ca:
sed -n '1d;/BEGIN/,/END/p' domain.crt > letsencrypt-ca.crt
task config --force taskd.ca "$PWD/letsencrypt-ca.crt"

If you don't have domain.crt in your client machine (it's a server-side
file after all), but you already set taskd properly, then you can do
the following on the client machine to generate letsencrypt-ca.crt:
gnutls-cli --print-cert -p 53589 domain.example.com </dev/zero \
| sed -n '/BEGIN/,/END/p' \
| sed -n '1d;/BEGIN/,/END/p' \
> letsencrypt-ca.crt

My sed-fu is a bit weak, so I decided to do the filtering in two steps,
the first to isolate the certificates, the second to remove the first
certificate and keep the second one.
The last command above can be useful to update file letsencrypt-ca.crt
when needed (because it's a certificate that will eventually expire).
Summing up:


generate a key domain.key


setup a client for Let's Encrypt to get a certificate domain.crt


extract letsencrypt-ca.crt from domain.crt, either directly or
using gnutls-cli and some sed magic


do the following configurations on the server:
  taskd config --force server.key  /path/to/domain.key
  taskd config --force server.cert /path/to/domain.crt


do the folloiwing configuration on the client:
  task config --force taskd.ca /path/to/letsencrypt-ca.crt