Blob login, nonce, sig, pw, payload, hdr;
  const char *zSep;
  int i;
  int cnt = 0;

  blob_zero(&nonce);
  blob_zero(&pw);
  sha1sum_blob(pSend, &nonce);
  blob_copy(&pw, &nonce);
  blob_zero(&login);
  if( g.urlUser==0 ){
    user_select();
    db_blob(&pw, "SELECT pw FROM user WHERE uid=%d", g.userUid);
    sha1sum_blob(&pw, &sig);
    blob_appendf(&login, "login %s %b %b\n", g.zLogin, &nonce, &sig);

    const char *zUuid = db_column_text(&q, 0);
    blob_appendf(pXfer->pOut, "gimme %s\n", zUuid);
    pXfer->nGimmeSent++;
  }
  db_finalize(&q);
}

/*
** Compute an SHA1 hash on the tail of pMsg.  Verify that it matches the
** the hash given in pHash.  Return 1 on a successful match.  Return 0
** if there is a mismatch.
*/
static int check_tail_hash(Blob *pHash, Blob *pMsg){
  Blob tail;
  Blob h2;
  int rc;
  blob_tail(pMsg, &tail);
  sha1sum_blob(&tail, &h2);
  rc = blob_compare(pHash, &h2);
  blob_reset(&h2);
  blob_reset(&tail);
  return rc==0;
}


/*
** Check the signature on an application/x-fossil payload received by
** the HTTP server.  The signature is a line of the following form:
**
**        login LOGIN NONCE SIGNATURE
**
** The NONCE is the SHA1 hash of the remainder of the input.  
** SIGNATURE is the SHA1 checksum of the NONCE concatenated 
** with the users password.
**
** The parameters to this routine are ephermeral blobs holding the
** LOGIN, NONCE and SIGNATURE.
**
** This routine attempts to locate the user and verify the signature.
** If everything checks out, the USER.CAP column for the USER table
** is consulted to set privileges in the global g variable.
**
** If anything fails to check out, no changes are made to privileges.
**
** Signature generation on the client side is handled by the 
** http_exchange() routine.
*/
void check_login(Blob *pLogin, Blob *pNonce, Blob *pSig){
  Stmt q;
  int rc;




  db_prepare(&q, "SELECT pw, cap, uid FROM user WHERE login=%B", pLogin);
  if( db_step(&q)==SQLITE_ROW ){
    Blob pw, combined, hash;
    blob_zero(&pw);
    db_ephemeral_blob(&q, 0, &pw);
    blob_zero(&combined);
    blob_copy(&combined, pNonce);

    ** The client can send multiple logins.  Permissions are cumulative.
    */
    if( blob_eq(&xfer.aToken[0], "login")
     && xfer.nToken==4
    ){
      if( disableLogin ){
        g.okRead = g.okWrite = 1;
      }else if( check_tail_hash(&xfer.aToken[2], xfer.pIn) ){
        check_login(&xfer.aToken[1], &xfer.aToken[2], &xfer.aToken[3]);
      }
    }else
    
    /*    cookie TEXT
    **
    ** A cookie contains a arbitrary-length argument that is server-defined.

cards.  Each login card has the following format:</p>

<blockquote>
<b>login</b>  <i>userid  nonce  signature</i>
</blockquote>

<p>The userid is the name of the user that is requesting service
from the server.  The nonce is the SHA1 hash of the remainder of
the message - all text that follows the newline character that
terminates the login card.  The signature is the SHA1 hash of
the concatenation of the nonce and the users password.</p>

<p>For each login card, the server looks up the user and verifies
that the nonce matches the SHA1 hash of the remainder of the
message.  It then checks the signature hash to make sure the 
signature matches.  If everything
checks out, then the client is granted all privileges of the
specified user.</p>

<p>Privileges are cumulative.  There can be multiple successful
login cards.  The session privileges are the bit-wise OR of the
privileges of each individual login.</p>