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012// ***************************************************************************************************************************
013package org.apache.juneau.http;
014
015/**
016 * Represents a parsed <l>Authorization</l> HTTP request header.
017 * 
018 * <p>
019 * Authentication credentials for HTTP authentication.
020 * 
021 * <h5 class='figure'>Example</h5>
022 * <p class='bcode'>
023 *    Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
024 * </p>
025 * 
026 * <h5 class='topic'>RFC2616 Specification</h5>
027 * 
028 * A user agent that wishes to authenticate itself with a server--usually, but not necessarily, after receiving a 401
029 * response--does so by including an Authorization request-header field with the request.
030 * 
031 * <p>
032 * The Authorization field value consists of credentials containing the authentication information of the user agent for
033 * the realm of the resource being requested.
034 * 
035 * <p class='bcode'>
036 *    Authorization  = "Authorization" ":" credentials
037 * </p>
038 * 
039 * <p>
040 * HTTP access authentication is described in "HTTP Authentication: Basic and Digest Access Authentication".
041 * 
042 * <p>
043 * If a request is authenticated and a realm specified, the same credentials SHOULD be valid for all other requests
044 * within this realm (assuming that the authentication scheme itself does not require otherwise, such as credentials
045 * that vary according to a challenge value or using synchronized clocks).
046 * 
047 * <p>
048 * When a shared cache (see section 13.7) receives a request containing an Authorization field, it MUST NOT return the
049 * corresponding response as a reply to any other request, unless one of the following specific exceptions holds:
050 * <ol>
051 *    <li>If the response includes the "s-maxage" cache-control directive, the cache MAY use that response in replying
052 *       to a subsequent request.
053 *       But (if the specified maximum age has passed) a proxy cache MUST first revalidate it with the origin
054 *       server, using the request-headers from the new request to allow the origin server to authenticate the new
055 *       request.
056 *       (This is the defined behavior for s-maxage.)
057 *       If the response includes "s-maxage=0", the proxy MUST always revalidate it before re-using it.
058 *    <li>If the response includes the "must-revalidate" cache-control directive, the cache MAY use that response in
059 *       replying to a subsequent request.
060 *       But if the response is stale, all caches MUST first revalidate it with the origin server, using the
061 *       request-headers from the new request to allow the origin server to authenticate the new request.
062 *    <li>If the response includes the "public" cache-control directive, it MAY be returned in reply to any subsequent
063 *       request.
064 * </ol>
065 * 
066 * <h5 class='section'>See Also:</h5>
067 * <ul class='doctree'>
068 *    <li class='extlink'><a class='doclink' href='https://www.w3.org/Protocols/rfc2616/rfc2616.html'>Hypertext Transfer Protocol -- HTTP/1.1</a>
069 * </ul>
070 */
071public final class Authorization extends HeaderString {
072
073   /**
074    * Returns a parsed <code>Authorization</code> header.
075    * 
076    * @param value The <code>Authorization</code> header string.
077    * @return The parsed <code>Authorization</code> header, or <jk>null</jk> if the string was null.
078    */
079   public static Authorization forString(String value) {
080      if (value == null)
081         return null;
082      return new Authorization(value);
083   }
084
085   private Authorization(String value) {
086      super(value);
087   }
088}