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  *      Authors: Jivka Bojilova
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  *    Copyright: 2000 Regents of the University of California and the
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  *               National Center for Ecological Analysis and Synthesis
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  * October Meeting SDSC, 2000
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<TITLE>Metacat</TITLE>
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  <table width="100%">
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    <tr>
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      <td class="tablehead" colspan="2"><p class="label">Metacat User 
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      Authentication and Access Control</p></td>
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      <td class="tablehead" colspan="2" align="right">
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        <a href="./xmlindex.html">Back</a> | <a href="./metacattour.html">Home</a> | 
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        <a href="./ldap.html">Next</a>
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  <p><b>Authentication</b></p>
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    <p>Metacat has a public interface for porting authentication 
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      schemes to Metacat.  Currently an LDAP scheme is implemented. 
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      LDAP stands for Lightweight Directory Access Protocol. 
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      It is an optimized database for fast retrival of stored data:
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      It is used by Metacat to store its users and their information. 
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      The users can be organized in one or more groups.
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    </p>
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    <P> <img src="auth.gif"> 
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    <P> <b>Access control in Metacat. </b></p>
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    <ul>
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      <li> Metacat users stored in the LDAP directory database are authenticated
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      to use Metacat services and resources.</li>
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      <li> A persistant session is assigned to an authenticated user.</li>
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      <li> Metacat also allows document level access control via Access Control 
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      Lists (ACLs).</li>
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    </ul>
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  <p style="color: red; font-face: bold">WARNING: The rest of this page is 
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   out-of-date and no longer accurate. It is left only for reference purposes.
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   ACL information is now set through EML 2.0.0 access control elements.
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  </p>
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  <!--<img src="acontrol.gif">-->
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  <b>ACLs</b>
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  <p>Metacat allows a user to set permissions for users or groups on individual 
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  documents by using
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  a special XML file called an Access file.  
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  The <a href="./packages.html">Package</a> file
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  specifies which documents the Access file refers to. 
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  A sample Access file looks like the following:</p>
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  <pre>
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    &lt;?xml version="1.0"?&gt;
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    &lt;!DOCTYPE acl PUBLIC "-//NCEAS//eml-access-2.0//EN" "eml-access-2.0.dtd"&gt;
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    &lt;acl authSystem="knb" order="allowFirst"&gt;
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      &lt;identifier&gt;nceas.36.1&lt;/identifier&gt;
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      &lt;allow&gt;
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        &lt;principal&gt;jones&lt;/principal&gt;
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        &lt;principal&gt;higgins&lt;/principal&gt;
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        &lt;principal&gt;berkley&lt;/principal&gt;
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        &lt;principal&gt;bojilova&lt;/principal&gt;
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        &lt;permission&gt;read&lt;/permission&gt;
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        &lt;duration&gt;
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          &lt;startDate&gt;10/9/2000&lt;/startDate&gt;
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          &lt;stopDate&gt;10/9/2001&lt;/stopDate&gt;
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        &lt;/duration&gt;
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        &lt;ticketCount&gt;100&lt;/ticketCount&gt;
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      &lt;/allow&gt;
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      &lt;allow&gt;
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        &lt;principal&gt;bojilova&lt;/principal&gt;
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        &lt;permission&gt;write&lt;/permission&gt;
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        &lt;ticketCount&gt;10&lt;/ticketCount&gt;
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      &lt;/allow&gt;
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      &lt;allow&gt;
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        &lt;principal&gt;reviewers&lt;/principal&gt;
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        &lt;permission&gt;read&lt;/permission&gt;
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        &lt;ticketCount&gt;5&lt;/ticketCount&gt;
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      &lt;/allow&gt;
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      &lt;allow&gt;
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        &lt;principal&gt;blankman&lt;/principal&gt;
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        &lt;permission&gt;all&lt;/permission&gt;
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      &lt;/allow&gt;
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      &lt;deny&gt;
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        &lt;principal&gt;eddins&lt;/principal&gt;
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        &lt;permission&gt;all&lt;/permission&gt;
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      &lt;/deny&gt;
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    &lt;/acl&gt;
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  </pre>
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  <p>This file is read into Metacat like any other XML file.  Like 
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     <a href="./packages.html">Packages</a> the doctype is checked against
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     the accessdoctype parameter in the <a href="./properties.html">Metacat
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     Properties</a> file.  If the doctype matches, special postprocessing
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     is performed on the document and the persmissions described in the file
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     are applied to the specified document.
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  </p>
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  <p>The main tag &lt;acl&gt; has attributes 'order' and 'authSystem'.  
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     Order refers to which permission type to process first, allow or deny.
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     The allowed values are "allowFirst" and  "denyFirst".  The default is "allowFirst".
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  </p>
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  <p>The &lt;identifier&gt; tag specifies the document identifier for the Access file
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     itself as stored in Metacat.
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  </p>
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  <p>Next are the permissions themselves.  An allow tag gives permissions to 
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  the specified user(s) (&lt;principal&gt;) and a deny tag takes the permissions
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  away from the user(s).  A principal should be a registered user or group.
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  A timed duration can be set on the permission after
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  which the user(s) will no longer have the specified permission.  A ticket count
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  can also be set.  This gives the user the number of accesses specified.  After
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  the user has accessed the document that number of times, the permissions are 
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  revoked. 
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  </p>
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