Make certificate uploadable instead of text input for SAML IDPs in passport

[jgomer2001]

When creating IDPs the certificate is required to be pasted as a single string with header, footer and blanks removed

The form should allow uploading the file or provide a textarea where cert contents can be pasted, then internally do the conversion as necessary.

[aliaksander-samuseu]

@syntrydy

Just wanted to share my thoughts on this. IMO it should allow both methods (an upload button AND text input field), as different IDPs may make the one or the other approach more convenient (can vary by IDP). Sometimes it's easier to copy-paste it, in other case uploading may be the easiest option.

Just one more thing: I would strongly suggest for the text input field to be able to digest a proper complete X.509 cert (as currently we need to strip BEGIN/END lines first, then turn it into one-liner, what is really cumbersome). As Passport apparently needs it to be a one-liner without those start-end tags, the code behind the field need to do all needed preparations transparently to the user.