view release on metacpan or  search on metacpan

lib/AWS/Signature/V4.pod  view on Meta::CPAN

the name of the built-in checksum, if any;

=item C<trailers>

hash reference from the name of each trailer that will be given to
L</finish> to the length of its value (e.g. C<12> for a base64-encoded
CRC-64). As in L</sign>, the trailer of C<checksum> must not be listed
here as well: declaring the same name twice is an error.

=back

=head2 The chunker

When streaming, L</sign> returns a C<chunker> that wraps the data
into chunks, signing them if needed. It keeps track of the amount of
data and of the signatures, so use it for one body only, and feed it the
data in order.

=head3 chunk

   my $encoded = $chunker->chunk($data);

Return the encoded version of a piece of data, to be sent as it is.
C<$data> is a byte string or a reference to one, it cannot be empty. It is
an error to go past the C<decoded_content_length>.

=head3 finish

   my $encoded = $chunker->finish(%trailer_values);

Return the final, empty chunk, followed by the trailers if any. It is an
error if the amount of data is not C<decoded_content_length>. The values
of the trailers declared in C<trailers> are passed by name, in any case;
it is an error to omit one, to pass one twice, to pass one that was not
declared or that is computed by the chunker, or to pass a value that is
not a byte string or has a CR, LF or NUL in it. After an error, the
chunker is as it was: C<finish> can be called again.


=head1 ERRORS

Errors are reported by throwing L<Ouch> exceptions (see C<< $@->code >>,
C<< $@->message >>). The code is C<400> when the problem is in what the
caller provided, e.g. a missing option, an invalid URL, a certificate that
cannot be read, a chunk that goes past the declared size; it is C<500>
when the fault is in the module itself, i.e. something that should not
happen whatever the input. The exception is reported at the line of the
caller, and its C<trace> does not include the arguments of the calls, as
they may hold secrets like passwords. Moo's own complaints, e.g. about the
arguments of the constructors that are not meant to be called directly,
are not Ouch exceptions.


=head1 SECURITY CONSIDERATIONS

=over

=item *

B<URLs.> A URL must be ASCII, without control characters and without user
information (C<user@host>): AWS endpoints never have it, and user agents
do not all agree on which host such a URL points to. For the same reason
the host can only be a name made of letters, digits, C<.>, C<_>, C<~>
and C<->, or an IP address, with an optional numeric port.

=item *

B<Authorize on what is signed.> For every service but S3 the path is
normalized before signing, as AWS does: C</public/../admin/delete> is
signed as C</admin/delete>, and that is what AWS executes. If your
application decides whether a caller may have a request signed by
looking at the URL, it must look at the normalized path (see the second
line of C<canonical_request>), not at the raw URL, or it can be bypassed.
For those same services, dot segments that are percent-encoded (e.g.
C<%2e%2e>) are an error, as it is not certain how AWS reads them; S3 does
not normalize at all, so there they are ordinary characters of the key and
C</public/%2e%2e/admin> is signed as it is.

=item *

B<Do not log the results.> C<headers> and C<authorization> can be used to
replay the request for up to 15 minutes; a presigned URL is a bearer token
until it expires; C<headers>, C<canonical_request> and presigned URLs
include the session token, if there is one. Treat them as secrets.

=item *

B<Secrets in memory.> The signer keeps the credentials (the secret access
key included) as long as it lives, and C<< ->credentials >> gives them
back. The text of an X.509 private key and its password are dropped once
the key is loaded. The key derived for signed chunks, which could sign
any request for the same service, region and day, is kept by the chunker
in a closure: no accessor gives back its bytes and dumping the chunker
does not show them, but whoever holds the chunker can still sign with it
through its internals. Do not hand the chunker, let alone the signer, to
code that you would not trust with the credentials.

=item *

B<Error messages> may include values that the caller provided, with
non-printable characters escaped (e.g. C<\x{A}>), so that they cannot
forge lines in a log.

=item *

B<Dependencies> are listed with their versions in F<cpanfile.snapshot>;
check them regularly against published advisories, e.g. with
L<CPAN::Audit>.

=back


=head1 BUGS AND LIMITATIONS

Minimum perl version 5.24.

Only Signature Version 4 is supported, not Version 4A (asymmetric,
multi-region). Event stream signing is not supported either.

Signing with the X.509 variant, including presigned URLs and the
transport of the certificate in the query string, follows the algorithm