code: public SharedAuthenticatedUser retrieveSharedConnectionUser(
              AuthenticationProvider authProvider, Credentials credentials) {
  
          // Validate the share key
          String shareKey = getShareKey(credentials);
          if (shareKey == null || connectionMap.get(shareKey) == null)
              return null;
  
          // Return temporary in-memory user
          return new SharedAuthenticatedUser(authProvider, credentials, shareKey);
  
      }
docs: Returns a SharedAuthenticatedUser if the given credentials contain a
  valid share key. The returned user will be associated with the single
  shared connection to which they have been granted temporary access. If
  the share key is invalid, or no share key is contained within the given
  credentials, null is returned.
  
  @param authProvider
  The AuthenticationProvider on behalf of which the user is being
  retrieved.
  
  @param credentials
  The credentials which are expected to contain the share key.
  
  @return
  A SharedAuthenticatedUser with access to a single shared connection,
  if the share key within the given credentials is valid, or null if
  the share key is invalid or absent.