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CA handler for Microsoft Certification Authority Web Enrollment Service

This CA handler uses Microsofts Certification Authority Web Enrollment service for certificate enrollment and modified version of the python library magnuswatn/certsrv for communication with the enrollment service.

When using the handler please be aware of the following limitations:

  • Authentication towards Web Enrollment Service is limited to "basic" "ntlm" or "gssapi" Kkerberos). There is currently no support for ClientAuth
  • Communication is limited to https
  • Revocation operations are not supported

Preparation

  1. Microsoft Certification Authority Web Enrollment Service must be enabled and configured - of course :-)
  2. You need to have a set of credentials with permissions to access the service and enrollment templates
  3. Authentication method (basic or ntlm) to the service must be configured correctly.
  4. (optional): In case you are installing from RPM and plan to use ntlm as authentication scheme you need two additonal python modules python3-request-ntlm and python3-ntlm-auth which are neither part of Standard nor the EPEL repo. If you have no clue from where to get these packaages feel free to use the ones being part of the a2c github repository
  5. (optional): In case you are installing from RPM and plan to use gssapi as authentication scheme you need two additonal python modules python3-request-gssapi and gssapi. If you have no clue from where to get these packaages feel free to use the ones being part of the a2c github repository

It is helpful to verify the service access before starting the configuration of acme2certifier

  • service access by using ntlm authentication towards certsrv
root@rlh:~# curl -I --ntlm --user <user>:<password> -k https://<host>/certsrv/
  • service access by using basic authentication
root@rlh:~# curl -I --user <user>:<password> -k https://<host>/certsrv/
  • service access by using gssapi authentication
root@rlh:~# export KRB5_CONFIG=<path>/krb5.conf
root@rlh:~# kinit <username>
root@rlh:~# curl --negotiate -u: <user>:<password> -k https://<host>/certsrv/

Access to the service is possible if you see the status code 200 returned as part of the response

HTTP/1.1 200 OK
Cache-Control: private
Content-Length: 3686
Content-Type: text/html
Server: Microsoft-IIS/10.0
Set-Cookie: - removed - ; secure; path=/
X-Powered-By: ASP.NET

Installation

  • you need to allow the md4 algorithm in openssl.cfg
$ sudo sed -i "s/default = default_sect/\default = default_sect\nlegacy = legacy_sect/g" /etc/ssl/openssl.cnf && \
$ sudo sed -i "s/\[default_sect\]/\[default_sect\]\nactivate = 1\n\[legacy_sect\]\nactivate = 1/g" /etc/ssl/openssl.cnf
  • install certsrv via pip (module is already part of the docker images)
root@rlh:~# pip install certsrv[ntlm]
  • modify the server configuration (/acme_srv/acme_srv.cfg) and add the following parameters
[CAhandler]
handler_file: examples/ca_handler/mscertsrv_ca_handler.py
host: <hostname>
user: <username>
password: <password>
ca_bundle: <filename>
auth_method: <basic|ntlm>
template: <name>
allowed_domainlist: ["example.com", "*.example2.com"]
krb5_config: <path_to_individual>/krb5.conf
eab_profiling: False
  • host - hostname of the system providing the Web enrollment service
  • host_variable - optional - name of the environment variable containing host address (a configured host parameter in acme_srv.cfg takes precedence)
  • user - username used to access the service
  • user_variable - optional - name of the environment variable containing the username used for service access (a configured user parameter in acme_srv.cfg takes precedence)
  • password - password
  • password_variable - optional - name of the environment variable containing the password used for service access (a configured password parameter in acme_srv.cfg takes precedence)
  • ca_bundle - CA certificate bundle in pem format needed to validate the server certificate
  • auth_method - authentication method (either "basic", "ntlm" or "gssapi")
  • krb5_config - optional - path to individual krb5.conf
  • template - certificate template used for enrollment
  • allowed_domainlist - optional - list of domain-names allowed for enrollment in json format example: ["bar.local$, bar.foo.local]
  • eab_profiling - optional - activate eab profiling (default: False)

Passing a template from client to server

The handler makes use of the header_info_list feature allowing an acme-client to specify a template name to be used during certificate enrollment. This feature is disabled by default and must be activate in acme_srv.cfg as shown below

[Order]
...
header_info_list: ["HTTP_USER_AGENT"]

The acme-client can then specify the temmplate name as part of its user-agent string.

Example for acme.sh:

docker exec -i acme-sh acme.sh --server http://<acme-srv> --issue -d <fqdn> --standalone --useragent template=foo --debug 3 --output-insecure

Example for lego:

docker run -i -v $PWD/lego:/.lego/ --rm --name lego goacme/lego -s http://<acme-srv> -a --email "lego@example.com" --user-agent template=foo -d <fqdn> --http run

eab profiling

This handler can use the eab profiling feture to allow individual enrollment configuration per acme-account as well as restriction of CN and SANs to be submitted within the CSR. The feature is disabled by default and must be activated in acme_srv.cfg

[EABhandler]
eab_handler_file: examples/eab_handler/kid_profile_handler.py
key_file: <profile_file>

[CAhandler]
eab_profiling: True

below an example key-file used during regression testing:

{
  "keyid_00": {
    "hmac": "V2VfbmVlZF9hbm90aGVyX3ZlcnkfX2xvbmdfaG1hY190b19jaGVja19lYWJfZm9yX2tleWlkXzAwX2FzX2xlZ29fZW5mb3JjZXNfYW5faG1hY19sb25nZXJfdGhhbl8yNTZfYml0cw",
    "cahandler": {
      "template": ["WebServerModified", "WebServer"],
      "allowed_domainlist": ["www.example.com", "www.example.org", "*.local"],
      "unknown_key": "unknown_value"
    }
  },
  "keyid_01": {
    "hmac": "YW5vdXRoZXJfdmVyeV9sb25nX2htYWNfZm9yX2tleWlkXzAxX3doaWNoIHdpbGxfYmUgdXNlZF9kdXJpbmcgcmVncmVzc2lvbg",
    "cahandler": {
      "template": "WebServerModified",
      "allowed_domainlist": ["www.example.com", "www.example.org", "*.local"],
      "unknown_key": "unknown_value"
    }
  },
  "keyid_02": {
    "hmac": "dGhpc19pc19hX3ZlcnlfbG9uZ19obWFjX3RvX21ha2Vfc3VyZV90aGF0X2l0c19tb3JlX3RoYW5fMjU2X2JpdHM",
    "cahandler": {
      "allowed_domainlist": ["www.example.com", "www.example.org"]
    }
  },
  "keyid_03": {
    "hmac": "YW5kX2ZpbmFsbHlfdGhlX2xhc3RfaG1hY19rZXlfd2hpY2hfaXNfbG9uZ2VyX3RoYW5fMjU2X2JpdHNfYW5kX3Nob3VsZF93b3Jr"
  }
}