Mail: added support for XOAUTH2 and OAUTHBEARER authentication. This patch adds support for the OAUTHBEARER SASL mechanism as defined by RFC 7628, as well as pre-RFC XOAUTH2 SASL mechanism. For both mechanisms, the "Auth-User" header is set to the client identity obtained from the initial SASL response sent by the client, and the "Auth-Pass" header is set to the Bearer token itself. The auth server may return the "Auth-Error-SASL" header, which is passed to the client as an additional SASL challenge. It is expected to contain mechanism-specific error details, base64-encoded. After the client responds (with an empty SASL response for XAUTH2, or with "AQ==" dummy response for OAUTHBEARER), the error message from the "Auth-Status" header is sent. Based on a patch by Rob Mueller.

<!ENTITY  nbsp         "&#xA0;" >
<!ENTITY  mdash        "&#xA0;- " >


<!ELEMENT change_log   (section)* >

<!ELEMENT section      (changes)* >
<!ATTLIST section      title  CDATA #REQUIRED >

<!ELEMENT changes      (change)* >
<!ATTLIST changes      ver    CDATA #REQUIRED
                       date   CDATA #REQUIRED
>

<!ELEMENT change       (para)* >
<!ATTLIST change       type (bugfix | feature | change | security | workaround) #IMPLIED >

<!ELEMENT para         (#PCDATA | at | br | nobr)* >
<!ATTLIST para         lang (ru | en) #REQUIRED >

<!ELEMENT at           EMPTY >
<!ELEMENT br           EMPTY >
<!ELEMENT nobr         (#PCDATA) >