AWS S3 Authentication plugin

This is a plugin for Apache Traffic Server that provides support for the Amazon S3 authentication features. This is useful if you for example want to use S3 as your origin server, yet want to avoid direct user access to the content.

Using the plugin

Using the plugin in a remap rule would be e.g.:

# remap.config

...  @plugin=s3_auth.so @pparam=--access_key @pparam=my-key \
                        @pparam=--secret_key @pparam=my-secret \
                        @pparam=--virtual_host

Alternatively, you can store the access key and secret in an external configuration file, and point the remap rule(s) to it:

# remap.config

...  @plugin=s3_auth.so @pparam=--config @pparam=s3_auth_v2.config

Where s3.config could look like:

# s3_auth_v2.config

access_key=my-key
secret_key=my-secret
version=2
virtual_host=yes

Both ways could be combined as well

AWS Authentication version 4

The s3_auth plugin fully implements: AWS Signing Version 4 / Authorization Header / Transferring Payload in a Single Chunk / Unsigned Payload Option

Configuration options:

# Mandatory options
--access_key=<access_id>
--secret_key=<key>
--version=4

# Optional
--v4-include-headers=<comma-separated-list-of-headers-to-be-signed>
--v4-exclude-headers=<comma-separated-list-of-headers-not-to-be-signed>
--v4-region-map=region_map.config

If the following option is used then the options could be specified in a file:

--config=s3_auth_v4.config

The s3_auth_v4.config config file could look like this:

# s3_auth_v4.config

access_key=<access_id>
secret_key=<secret_key>
version=4
v4-include-headers=<comma-separated-list-of-headers-to-be-signed>
v4-exclude-headers=<comma-separated-list-of-headers-not-to-be-signed>
v4-region-map=region_map.config

Where the region_map.config defines the entry-point hostname to region mapping i.e.:

# region_map.config

# "us-east-1"
s3.amazonaws.com                     : us-east-1
s3-external-1.amazonaws.com          : us-east-1
s3.dualstack.us-east-1.amazonaws.com : us-east-1

# us-west-1
s3-us-west-1.amazonaws.com           : us-west-1
s3.dualstack.us-west-1.amazonaws.com : us-west-1

# Default region if no entry-point matches:
: s3.amazonaws.com

If --v4-region-map is not specified the plugin defaults to the mapping defined in “Regions and Endpoints - S3”

According to Transferring Payload in a Single Chunk specification the CanonicalHeaders list must include the Host header, the Content-Type header if present in the request and all the x-amz-* headers so --v4-include-headers and --v4-exclude-headers do not impact those headers and they are always signed.

The Via and X-Forwarded-For headers are always excluded from the signature since they are meant to be changed by the proxies and signing them could lead to invalidation of the signatue.

If --v4-include-headers is not specified all headers except those specified in --v4-exclude-headers will be signed.

If --v4-include-headers is specified only the headers specified will be signed except those specified in --v4-exclude-headers

AWS Authentication version 2

For more details on the S3 auth version 2 , see: Signing and Authenticating REST Requests

There are 4 plugin configuration options for version 2:

--access_key    <access_id>
--secret_key    <secret_key>
--virtual_host
--config        <config file>
--version=2

This is a pretty barebone start for the S3 services, it is missing a number of features:

  • It does not do UTF8 encoding (as required)
  • It does not deal with canonicalization of AMZ headers.
  • It does not handle POST requests (but do we need to ?)
  • It does not incorporate query parameters.

Contributions to any of these would be appreciated.