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IPA Client Design

To be able to request a certificate from the IPA client automatically
there should be a utility tightly integrated with the IPA client that
would aid in requesting the certificate for a service running on the
host. The following diagram shows all the IPA client components involved
in the operation. 

  ┌───────────────┐
  │  ipa-getcert  │
  │    utility    │
  └───────────────┘
          │
          │ D-Bus interface
          │
   ┌──────────────┐                                       ┌──────────┐
   │  certmonger  │                                       │          │
   │    system    │────── XML-RPC Connection to IPA ──────│  IPA CA  │
   │    daemon    │                                       │          │
   └──────────────┘                                       └──────────┘

1. The cert utility, named ipa-getcert in the diagram, will accept
   command line parameters and issue requests to certmonger. This is the
   only thing it will do. 
2. The daemon will be event-based, like most other services on the
   client designed so far.  It will respond to requests from the
   ipa-getcert client, and if necessary, poll for completion of any
   time-consuming tasks that it has started.  Such tasks include:
   * key generation
   * generating certificate signing requests (CSRs)
   * submitting signing requests to CAs
3. The daemon keeps track of its own work items.  The client can afford
   to be rather dumb by comparison.
4. As an implementation detail, the daemon talks to the CA by means of a
   helper which it runs.  The helper can also be run directly for
   troubleshooting purposes, and even replaced entirely.

Command Line Utility

Now it's time to talk about how ipa-getcert is used.  At its core, the
tool's function is analogous to that of ipa-getkeytab, so we're aiming
for a command-line interface which feels familiar.

There are five general tasks which the tool needs to be able to do:
  * Request a new certificate and track (by default or not, if told not
    to) its expiration date.
  * Resubmit a previously-denied enrollment request.
  * Start tracking expiration for an already-provisioned certificate.
  * Stop tracking expiration for an already-provisioned certificate.
  * Status: list current pending requests and/or currently tracked certs
    and the set of known CAs.

In the case of requesting a certificate the command looks like this:

  ipa-getcert request [options]

  Required arguments:
  * If using an NSS database for storage:
    -d DIR      NSS database for key and cert
    -n NAME     nickname for NSS-based storage (only valid with -d)
    -t NAME     optional token name for NSS-based storage (only valid with -d)
  * If using files for storage:
    -k FILE     PEM file for private key
    -f FILE     PEM file for certificate (only valid with -k)

  Optional arguments:
  * Certificate handling settings:
    -I NAME     nickname to assign to the request
    -g SIZE     size of key to be generated if one is not already in place
    -r          attempt to renew the certificate when expiration nears (default)
    -R          don't attempt to renew the certificate when expiration nears
    -c CA       use the specified CA rather than the default (IPA's)
  * Parameters for the signing request:
    -N NAME     set requested subject name (default: CN=<hostname>)
    -U EXTUSAGE set requested extended key usage OID
    -K NAME     set requested principal name
    -D DNSNAME  set requested DNS name
    -E EMAIL    set requested email address

  The simplest invocation might look like this:

  ipa-getcert -d /etc/pki/nssdb -n "ServerCert"

In case of starting to track a certificate's expiration, one shall
provide the following command line: 

  ipa-getcert start-tracking [options]

  Required arguments:
  * If modifying an existing request:
    -i NAME    nickname of an existing tracking request
  * If using an NSS database for storage:
    -d DIR     NSS database for key and cert
    -n NAME    nickname for NSS-based storage (only valid with -d)
    -t NAME    optional token name for NSS-based storage (only valid with -d)
  * If using files for storage:
    -k FILE    PEM file for private key
    -f FILE    PEM file for certificate (only valid with -k)

  Optional arguments:
  * Certificate handling settings:
    -I NAME    nickname to give to tracking request
    -r         attempt to renew the certificate when expiration nears (default)
    -R         don't attempt to renew the certificate when expiration nears
    -c CA      use the specified CA rather than the default

  If there's no certificate in the specified location, the daemon will
  attempt to have one issued.  The daemon will cache information about
  the certificate for bookkeeping.

In case of stopping the tracking of a certificate's expiration, it would
be more like this:

  Usage: getcert stop-tracking [options]

  Required arguments:
  * By request identifier:
    -i NAME    nickname for tracking request
  * If using an NSS database for storage:
    -d DIR     NSS database for key and cert
    -n NAME    nickname for NSS-based storage (only valid with -d)
    -t NAME    optional token name for NSS-based storage (only valid with -d)
  * If using files for storage:
    -k FILE    PEM file for private key
    -f FILE    PEM file for certificate (only valid with -k)

The status commands list the work items that the daemon is tracking.

  Usage: getcert list [options]

  Optional arguments:
  * General options:
    -c CA   list only requests and certs associated with this CA
    -r      list only information about in-progress enrollment requests
    -t      list only information about tracked certificates