Caching suggestion to avoid phantom logons

[andrew-k-21-12]

Not sure about it, but maybe we should add here some cache-preventing headers:

node-samlp/lib/samlp.js

Line 152 in 69a1806

res.set('Content-Type', 'text/html');

Otherwise browsers use a cached response and complete a logon if we just press a back button (even if we are now in a logged out state). Thank you.