RubySaml::Utils::format_cert mishandles extra text outside of PEM block.

[netapp-mraymond]

RFC 7468 says "Data before the encapsulation boundaries are permitted" in a PEM format file. But the code in
https://github.com/onelogin/ruby-saml/blob/c38d72425b11aee5b2be595d44b407f8dfd92d6a/lib/onelogin/ruby-saml/utils.rb#L85
, when given a file with a single PEM block of certificate plus some non-ASCII extra text, will reformat in such way to move those extra text into the PEM block, resulting in downstream failures to decode.

[johnnyshields]

I think it is reasonable to support stripping out everything prior to --- BEGIN --- and --- END --. Should check if there is a RFC 7468-compliant function already. This would be a good to do for RubySaml 2.0

[pitbulk]

@johnnyshields At php-saml support for certs with comments was added:
SAML-Toolkits/php-saml@a08c168

But someone opened a potential issue so not sure if the implementation is 100% ok.

[johnnyshields]

@netapp-mraymond I have a fix in #711 that hopefully will make it into 2.0