    Granting Example
    ================

    In this example, we look at granting (or denying) principals (or
    roles) to principals.

    To make grants, we visit grant.html.  This doesn't display any
    grant information until we select a principal.

      >>> print http(r"""
      ... GET /@@grant.html HTTP/1.1
      ... Authorization: Basic mgr:mgrpw
      ... Referer: http://localhost:8081/@@contents.html
      ... """)
      HTTP/1.1 200 Ok
      ...

    If we submit a search request, we'll get a list of principals, from
    which we can choose:

      >>> print http(r"""
      ... POST /@@grant.html HTTP/1.1
      ... Authorization: Basic mgr:mgrpw
      ... Content-Length: 117
      ... Content-Type: application/x-www-form-urlencoded
      ... Referer: http://localhost:8081/@@grant.html
      ...
      ... field.principal.displayed=y"""
      ... "&field.principal.MA__.searchstring="
      ... "&field.principal.MA__.search=Search")
      HTTP/1.1 200 Ok
      ...
Manager
      ...

    We can then choose one.  If we do so, we get output that includes form
    elements for inputing security settings:

      >>> print http(r"""
      ... POST /@@grant.html HTTP/1.1
      ... Authorization: Basic mgr:mgrpw
      ... Content-Length: 62415
      ... Content-Type: application/x-www-form-urlencoded
      ... Referer: http://localhost:8081/@@grant.html
      ...
      ... field.principal.displayed=y"""
      ... """&field.principal.MA__.searchstring="""
      ... """&field.principal.MA__.selection=em9wZS5tZ3I_"""
      ... """&field.principal.MA__.apply=Apply""")
      HTTP/1.1 200 Ok
      ...
...
      ...

    Before we submit any data, there are no grants for the root object
    except for a one made by the testing framework that grants the manager
    role to the test manager:

      >>> root = getRootFolder()
      >>> import zope.app.securitypolicy.interfaces
      >>> grants = zope.app.securitypolicy.interfaces.IGrantInfo(root)
      >>> grants.principalPermissionGrant('zope.mgr', 'zope.ManageCode')
      PermissionSetting: Unset
      >>> list(grants.getRolesForPrincipal('zope.mgr'))
      [('zope.Manager', PermissionSetting: Allow)]

    Now, we can submit changes. (I've actually reduced the form input
    to just the things we want to change to both limit the text here and
    to reduce dependencies on specific roles and permissions:

      >>> print http(r"""
      ... POST /@@grant.html HTTP/1.1
      ... Authorization: Basic mgr:mgrpw
      ... Content-Length: 62437
      ... Content-Type: application/x-www-form-urlencoded
      ... Referer: http://localhost:8081/@@grant.html
      ...
      ... field.principal=em9wZS5tZ3I_"""
      ... """&field.principal.displayed=y"""
      ... """&field.principal.MA__.searchstring="""
      ... """&field.em9wZS5tZ3I_.role.zope.Member=allow"""
      ... """&field.em9wZS5tZ3I_.role.zope.Member-empty-marker=1"""
      ... """&field.em9wZS5tZ3I_.permission.zope.ManageCode=deny"""
      ... """&field.em9wZS5tZ3I_.permission.zope.ManageCode-empty-marker=1"""
      ... """&GRANT_SUBMIT=Change""")
      HTTP/1.1 200 Ok
      ...
...
      ...

    And, if we check the grants, we see the changes:

      >>> grants = zope.app.securitypolicy.interfaces.IGrantInfo(root)

      >>> grants.principalPermissionGrant('zope.mgr', 'zope.ManageCode')
      PermissionSetting: Deny

      >>> role_grants = list(grants.getRolesForPrincipal('zope.mgr'))
      >>> role_grants.sort()
      >>> role_grants
      ... # doctest: +NORMALIZE_WHITESPACE
      [('zope.Manager', PermissionSetting: Allow),
       ('zope.Member', PermissionSetting: Allow)]