This is exactly the problem which TLSNotary/PageSigner solves. You can show your online bank statement page without handing over your login credentials.
https://tlsnotary.org/pagesigner.html
https://tlsnotary.org/pagesigner.html
This is interesting. Are you the dev? The quick start video there is even using bitcointalk as an example!
I am not a programmer, but open source gives the tlsnotary add-on a bit more credibility. I might not use this for bank accounts yet, could be handy for verifying a PM on the forum. Thanks.