Swan at my back door

I write in the hope that someone that help. 

This afternoon a adult Swan came wondering into my back garden. We feed him/her some bread (3 slices) and then it kept wondering around the area. 

However, now it has settled down at my glass back door and I am worried if it is OK. 

Would be really grateful if some can advise. 

Many thanks in advance. 

Regards...