STORE: split off the description of the 'file' scheme loader

=pod

=begin comment

This is a recommended way to describe OSSL_STORE loaders,

"ossl_store-{name}", where {name} is replaced with the name of the

scheme it implements, in man section 7.

=end comment

=head1 NAME

ossl_store-file - The store 'file' scheme loader

=head1 SYNOPSIS

=for comment generic

#include <openssl/store.h>

=head1 DESCRIPTION

Support for the 'file' scheme is built into C<libcrypto>.

Since files come in all kinds of formats and content types, the 'file'

scheme has its own layer of functionality called "file handlers",

which are used to try to decode diverse types of file contents.

In case a file is formatted as PEM, each called file handler receives

the PEM name (everything following any 'C<-----BEGIN >') as well as

possible PEM headers, together with the decoded PEM body.  Since PEM

formatted files can contain more than one object, the file handlers

are called upon for each such object.

If the file isn't determined to be formatted as PEM, the content is

loaded in raw form in its entirety and passed to the available file

handlers as is, with no PEM name or headers.

Each file handler is expected to handle PEM and non-PEM content as

appropriate.  Some may refuse non-PEM content for the sake of

determinism (for example, there are keys out in the wild that are

represented as an ASN.1 OCTET STRING.  In raw form, it's not easily

possible to distinguish those from any other data coming as an ASN.1

OCTET STRING, so such keys would naturally be accepted as PEM files

only).

=head1 NOTES

When needed, the 'file' scheme loader will require a pass phrase by

using the C<UI_METHOD> that was passed via OSSL_STORE_open().

This pass phrase is used as it is, which may present some challenge

when the file that's loaded contains a PKCS#12 object.

See L<passphrase-encoding(7)> for more information.

=begin comment

The treatment of pass phrases is currently being worked on and may

change.

=end comment

=head1 SEE ALSO

L<ossl_store(7)>, L<passphrase-encoding(7)>

=head1 COPYRIGHT

Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License").  You may not use

this file except in compliance with the License.  You can obtain a copy

in the file LICENSE in the source distribution or at

L<https://www.openssl.org/source/license.html>.

=cut

Support for a URI scheme is called a STORE "loader", and can be added

dynamically from the calling application or from a loadable engine.

=head2 The 'file' scheme

Support for the 'file' scheme is already built into C<libcrypto>.

Since files come in all kinds of formats and content types, the 'file'

scheme has its own layer of functionality called "file handlers",

which are used to try to decode diverse types of file contents.

In case a file is formatted as PEM, each called file handler receives

the PEM name (everything following any 'C<-----BEGIN >') as well as

possible PEM headers, together with the decoded PEM body.  Since PEM

formatted files can contain more than one object, the file handlers

are called upon for each such object.

If the file isn't determined to be formatted as PEM, the content is

loaded in raw form in its entirety and passed to the available file

handlers as is, with no PEM name or headers.

Each file handler is expected to handle PEM and non-PEM content as

appropriate.  Some may refuse non-PEM content for the sake of

determinism (for example, there are keys out in the wild that are

represented as an ASN.1 OCTET STRING.  In raw form, it's not easily

possible to distinguish those from any other data coming as an ASN.1

OCTET STRING, so such keys would naturally be accepted as PEM files

only).

Support for the 'file' scheme is built into C<libcrypto>.

See L<ossl_store-file(7)> for more information.

=head1 EXAMPLES