Hello,
I am using the ddclient perl script to update my ip, but it seems that my username and password are always rejected.
username and password are configured in /etc/ddclient.conf on my debian system.

When I try with
# ddclient -daemon=0 -debug -verbose -noquiet
The result is
(...)
DEBUG: proxy =
DEBUG: url = checkip.dynu.com/
DEBUG: server = checkip.dynu.com
CONNECT: checkip.dynu.com
CONNECTED: using HTTP
SENDING: GET / HTTP/1.0
SENDING: Host: checkip.dynu.com
SENDING: User-Agent: ddclient/3.8.2
SENDING: Connection: close
SENDING:
RECEIVE: HTTP/1.1 200 OK
RECEIVE: Date: Wed, 19 Apr 2017 23:10:17 GMT
RECEIVE: Server: Apache/2.4.6 (CentOS) OpenSSL/1.0.1e-fips PHP/5.4.16
RECEIVE: X-Powered-By: PHP/5.4.16
RECEIVE: Content-Length: 34
RECEIVE: Connection: close
RECEIVE: Content-Type: text/html; charset=UTF-8
RECEIVE:
RECEIVE: Current IP Address: 81.164.162.130
DEBUG: get_ip: using web, checkip.dynu.com/ reports 81.164.162.130
INFO: forcing updating haezebrouck.dynu.com because no cached entry exists.
DEBUG:
DEBUG: nic_dyndns2_update -------------------
INFO: setting IP address to 81.164.162.130 for haezebrouck.dynu.com
UPDATE: updating haezebrouck.dynu.com
DEBUG: proxy =
DEBUG: url = http://api.dynu.com/nic/update?system=dyndns&hostname=haezebrouck.dynu.com&myip=81.164.162.130
DEBUG: server = api.dynu.com
CONNECT: api.dynu.com
CONNECTED: using SSL
SENDING: GET /nic/update?system=dyndns&hostname=haezebrouck.dynu.com&myip=81.164.162.130 HTTP/1.0
SENDING: Host: api.dynu.com
SENDING: Authorization: Basic obcuredforsecurityreasons==
SENDING: User-Agent: ddclient/3.8.2
SENDING: Connection: close
SENDING:
RECEIVE: HTTP/1.1 200 OK
RECEIVE: Date: Wed, 19 Apr 2017 16:10:8 GMT
RECEIVE: Server: Dynu Web Server
RECEIVE: X-Powered-By: Dynu Dynamic DNS Service
RECEIVE: Content-Length: 7
RECEIVE: Content-Type: text/html
RECEIVE:
RECEIVE: badauth
FAILED: updating haezebrouck.dynu.com: badauth: Bad authorization (username or password)

The content of ddclientconfig

syslog=yes
protocol=dyndns2
use=web, web=checkip.dynu.com/, web-skip='IP Address'
server=api.dynu.com
login=loginUsedOnTheWebsite
password=passwordUsedOnTheWebsite
mail=root
mail-failure=root
daemon=7200
ssl=yes
placeholderforname.dynu.com


I tried with
password=passwordUsedOnTheWebsite
and
password='passwordUsedOnTheWebsite'

Should I configure a password for the ddclient somewhere, that is different from the password used to login to the website?

The authentication error is caused by the wrong hostname. The hostname you have in your account is haezebrouck.dynu.net, not haezebrouck.dynu.com.

That was the problem indeed. I totally overlooked that.

Thanks!