code: func (l *ConnectionsLimiter) AcquireConnection(token string) error {
  	l.Lock()
  	defer l.Unlock()
  
  	if l.maxConnections == 0 {
  		return nil
  	}
  
  	numberOfConnections, exists := l.connections[token]
  	if !exists {
  		l.connections[token] = 1
  		return nil
  	}
  	if numberOfConnections >= l.maxConnections {
  		return trace.LimitExceeded(
  			"too many connections from %v: %v, max is %v",
  			token, numberOfConnections, l.maxConnections)
  	}
  	l.connections[token] = numberOfConnections + 1
  	return nil
  }
docs: // AcquireConnection acquires connection and bumps counter