/ 
Amazon-Credentials-1.1.9
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/ Amazon::Credentials

NAME

Amazon::Credentials - fetch Amazon credentials from file, environment or role

SYNOPSIS

my @order = qw{ env file container role };
my $creds = Amazon::Credentials->new( { order => \@order } );

DESCRIPTION

Class to find AWS credentials from either the environment, configuration files, instance meta-data or container role.

You can specify the order using the order option in the constructor to determine the order in which the class will look for credentials. The default order is environent, file, container, instance meta-data. See "new".

VERSION

This document reverse to verion 1.1.9 of Amazon::Credentials.

METHODS AND SUBROUTINES

new

new( options );

my $aws_creds = Amazon::Credential->new( { profile => 'sandbox', debug => 1 });

options is a hash of keys that represent various options you can pass to the constructor to control how it will look for credentials. Any of the options can also be retrieved using their corresponding 'get_{option} method.

options

aws_access_key_id

AWS access key.

aws_secret_access_key

AWS secret access key.

Note: If you pass the access keys in the constructor then the constructor will not look in other places for credentials.

cache

boolean when set to false will prevent Amazon::Credentials from cacheing credentials. Cacheing is enabled by default.

Note that the if cacheing is disabled, the module will obtain credentials on the first call to one of the getters (get_aws_secret_access_key, get_aws_access_key_id or get_token). After each method call to retrieve the credential it will be removed. However, for a brief period before all of them have been accessed by the getter credentials will be locally stored.

If you use the credential_keys method for retrieving credentials, the entire tuple of credentials will be immediately passed to you without cacheing (if cacheing is disabled).

container

If the process is running in a container, this value will contain 'ECS' indicating that the credentials were optained for the task role. The class will look for credentials using the container metadata service:

http://169.254.170.2/$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI
debug

Set to true for verbose troubleshooting information. Set logger to a logger that implements a logging interface (ala Log::Log4perl.

decrypt

Reference to a custom method that will decrypt credentials prior to returning them from the cache. The method will be passed the string to decrypt and a passkey.

encrypt

Reference to a custom method that will encrypt credentials prior to storing them in the cache. The method will be passed a string to encrypt and the passkey.

env - Environment

If there exists an environment variable $AWS_PROFILE, then an attempt will be made to retrieve credentials from the credentials file using that profile, otherwise the class will for these environment variables to provide credentials.

AWS_ACCESS_KEY_ID
AWS_SECRET_ACCESS_KEY
AWS_SESSION_TOKEN

Note that when you set the environment variable AWS_PROFILE, the order essentially is overridden and the class will look in your credential files (~/.aws/config, ~/.aws/credentials) to resolve your credentials.

file - Configuration Files
~/.aws/config
~/.aws/credentials

The class will attempt to resolve credentials by interpretting the information in these two files. You can also specify a profile to use for looking up the credentials by passing it into the constructor or setting it the environment variable AWS_PROFILE. If no profile is provided, the default credentials or the first profile found is used.

my $aws_creds = Amazon::Credentials->new({ order => [qw/environment role file/] });
insecure

A debugging mode can be enabled to display information that may aid in troubleshooting, however output may include credentials. This attribute prevents accidental exfiltration of credentials during troubleshooting. The default setting of insecure is therefore false. This will prevent debug messages that may contain credentials (HTTP response, configuration file contents) from exposing sensitive data.

Set the value to 1 to enable all debug output except the content of credentials in HTTP responses. Set the value to 2 to enable full debug output.

Note that setting the value to 1 will enable the use of regular expressions to suppress credential contents. Credentials that do not conform to these may still be exposed. Caution is advised.

logger

Pass in your own logger that has a debug() method. Otherwise the default logger will output debug messages to STDERR.

order

An array reference containing tokens that specifies the order in which the class will search for credentials.

default: env, role, container, file

Example:

my $creds = Amazon::Credentials->new( { order => [ qw/file env role/] });
passkey

A custom passkey for encryption. You can pass a scalar or a reference to a subroutine that returns the passkey. The return value of the subroutine should be idempotent, however you can change the subroutine used for encryption if you are not cacheing the credentials. If you are cacheing credentials you should reset the credentials with the new passkey method.

$credentials->set_passkey(\&new_passkey_provider);
$credentials->reset_credentials(1);

Whether to print the error if no credenials are found. raise_error implies print_error.

default: true

profile

The profile name in the configuration file (~/.aws/config or ~/.aws/credentials).

my $aws_creds = Amazon::Credentials->new({ profile => 'sandbox' });

The class will also look for the environment variable AWS_PROFILE, so you can invoke your script like this:

$ AWS_PROFILE=sandbox my-script.pl
raise_error

Whether to raise an error if credentials are not found.

default: true

region

Default region. The class will attempt to find the region in either the configuration files or the instance unless you specify the region in the constructor.

role - Instance Role

The class will use the http://169.254.169.254/latest/meta-data/iam/security-credential URL to look for an instance role and credentials.

Credentials returned by accessing the meta-data include a token that should be passed to Amazon APIs along with the access key and secret. That token has an expiration and should be refreshed before it expires.

if ( $aws_creds->is_token_expired() ) {
  $aws_creds->refresh_token()
}
timeout

When looking for credentials in metadata URLs, this parameter specifies the timeout value for LWP. The default is 3 seconds.

user_agent

Pass in your own user agent, otherwise LWP will be used. Probably only useful to override this for testing purposes.>

as_string

as_string()

Returns the credentials as a JSON encode string.

credential_keys

my $credential_keys = $creds->credential_keys;

Return a hash reference containing the credential keys with standard key names. Note that the session token will only be present in the hash for temporary credentials.

AWS_ACCESS_KEY_ID
AWS_SECRET_ACCESS_KEY
AWS_SESSION_TOKEN

format_credentials

format_credentials(format-string)

Returns the credentials as a formatted string. The <format> argument allows you to include a format string that will be used to output each of the credential parts.

format("export %s=%s\n");

The default format is a "%s %s\n".

find_credentials

find_credentials( option => value, ...);

You normally don't want to use this method. It's automatically invoked by the constructor if you don't pass in any credentials. Accepts a hash or hash reference consisting of keys (order or profile) in the same manner as the constructor.

get_creds_from_*

These methods are called internally when the new constructor is invoked. You should never need to call these methods. All of these methods will return a hash of credential information and metadata described below.

aws_access_key_id

The AWS access key.

aws_secret_access_key

The AWS secret key.

token

Security token used with access keys.

expiration

Token expiration date.

role

IAM role if available.

source

The source from which the credentials were found.

  • IAM - retrieved from container or instance role

  • container - 'ECS' if retrieved from container

  • file - retrieved from file

  • process - retrieved from an external process

  • ENV - retrieved from environment

get_creds_from_container

get_creds_from_container()

Retrieves credentials from the container's metadata at http://169.254.170.2. Returns a hash of credentials containing:

aws_access_key_id
aws_secret_access_key
aws_session_token

Returns an empty hash if no credentials found. The environment variable AWS_CONTAINER_CREDENTIALS_RELATIVE_URI must exist or you must pass the value of the path as an argument.

get_creds_from_process

get_creds_from_process(process)

Retrieves credentials from a helper process defined in the config file. Returns the credentials tuple.

get_creds_from_role

get_creds_from_role()

Returns a hash, possibly containing access keys and a token.

get_default_region

Returns the region of the currently running instance or container. The constructor will set the region to this value unless you set your own region value. Use get_region to retrieve the value after instantiation or you can call this method again and it will make a second call to retrieve the instance metadata.

get_ec2_credentials (deprecated)

See "find_credentials"

is_token_expired

is_token_expired( window-interval )

Returns true if the token is about to expire (or is expired). window-interval is the time in minutes before the actual expiration time that the method should consider the token expired. The default is 5 minutes. Amazon states that new credentials will be available at least 5 minutes before a token expires.

reset_credentials

By default this method will remove credentials from the cache if you pass a false or no value. Passing a true value will refresh your credentials from the original source (equivalent to calling set_credentials).

refresh_token (deprecated)

use refresh_credentials()

refresh_credentials()

Retrieves a fresh set of IAM credentials.

if ( $creds->is_token_expired ) {
  $creds->refresh_token()
}

set_credentials

Looks for your credentials according to the order specified by the order attribute passed in the constructor and stores the credentials in the cache.

Note that you should never have to call this method. If you call this method it will ignore your cache setting!

SETTERS/GETTERS

All of the options described in the new method can be accessed by a getter or set using a setter of the same name.

Example:

$creds->set_cache(0);

DIAGNOSTICS

Set the debug option when you instantiate a Amazon::Credentials object to output debug and diagnostic messages. Note that you must also set the insecure option if you want to output full diagnostics. WARNING: Full diagnostics may include credentials. Be careful not to expose these values in logs.

CONFIGURATION AND ENVIRONMENT

The module will recognize several AWS specific environment variables described throughout this documentation.

AWS_ACCESS_KEY_ID
AWS_SECRET_ACCESS_KEY
AWS_SESSION_TOKEN
AWS_REGION
AWS_DEFAULT_REGION
AWS_CONTAINER_CREDENTIALS_RELATIVE_URI

BUGS AND LIMITATIONS

Amazon::Credentials will not attempt to retrieve temporary credentials for profiles that specify a role. If for example you define a role in your credentials file thusly:

[developer]

 role_arn = arn:aws:iam::123456789012:role/developer-access-role
 source_profile = dev

The module will not return credentials for the developer profile. While it would be theoretically possible to return those credentials, in order to assume a role, one needs credentials (chicken and egg problem).

DEPENDENCIES

Lower versions of these modules may be acceptable.

'Class::Accessor::Fast' => '0.31'
'Config::Tiny'          => '2.28'
'Date::Format'          => '2.24'
'File::HomeDir'         => '1.00'
'File::chdir'           => '0.1010'
'HTTP::Request'         => '6.00'
'List::Util'            => '1.5'
'LWP::UserAgent'        => '6.36'
'POSIX::strptime'       => '0.13'

...and possibly others

In order to enable true encryption of your credentials when cached, Crypt::CBC is also required.

SECURITY CONSIDERATIONS

The security concern around your credentials is not actually the fact that the credentials can be retrieved and viewed - any process that compromises your environment can use the same methods this class does to resolve those credentials. Let me repeat that. If your environment is compromised then an actor can use all of the methods employed in this module to access your credentials.

The major issue you should be concerned about is exposing your credentials outside of the environment running your program. Thats is, the exfiltration of your credentials. Once you have resolved these credentials you may inadvertantly reveal them in many ways. Dumping objects to logs, saving your credentials in files or even outputing them to your console may expose your credentials. This module will now at the very least obfuscate them when they are stored in memory. Accidental dumping of objects will not reveal your credentials in plain-text.

Always take precautions to prevent accidental exfiltration of your credentials.

How Amazon::Credentials Helps Prevent Exfiltration

For performance and historical reasons the default is for Amazon::Credentials to cache your credentials. Starting with version 1.1.0, the module will attempt to encrypt the credentials before storing them. The module uses Crypt::CBC (if available) with the default cipher and a random (or user defined) passkey.

Even if Crypt::CBC is not available, the module will try to obfuscate the credentials. A determined actor can still decrypt these keys if they have access to the obfuscated values and your passkey. You have several options to better secure your credentials from exposure.

Option 1 - Do not cache your credentials.

Use the set_cache() method with a false value or set cache to false when you instantiate the class. The default is to cache credentials.

my $credentials = Amazon::Credentials->new(cache => 0);

Normally, your credentials are fetched when the Amazon::Credentials object is instantiated. With cacheing turned off credentials will not be fetched until they are first requested.

There are two ways your programs typically will fetch the keys; either using the getter methods on the individual credentials keys or by retrieving a hash containing all of the keys.

credential_keys()

Use the method credential_keys to retrieve all of the keys at once as a hash. Using this method with cacheing turned off will prevent Amazon::Credentials from ever saving your credentials to variables that can be inadvertantly exposed. Each subsequent request for the keys will cause Amazon::Credentials to fetch the keys again.

Getter Methods

If you use the individual getters (get_aws_access_key_id, get_aws_secret_access_key and get_token), the keys will first be fetched and stored. As each getter is called the key will be removed (burn after reading, so to speak). Therefore, for a brief period your credentials will be cached even if cacheing is turned off.

Option 2 - Remove them manually after use

Call the reset_credentials() with a false value after fetching credentials or after they are used by downstream processes. Call the reset_credential() method with a true value to regenerate credentials.

Option 3 - Encrypt your credentials

Amazon::Credentials will encrypt your credentials by default starting with version 1.1.0. If Crypt::CBC is available, the class will use the default cipher and a random passkey to encrypt your credentials. If the encryption module is not available, the class will still obfuscate (not encrypt) the credentials. Encryption when the passkey and method used are known to a determined bad actor is no better than obfuscation. Accordingly, there are several ways you can and should encrypt credentials in a more secure way.

Using a Custom passkey

By default the module will generate its own random passkey during initialization and use that to encrypt and decrypt the credentials. Obviously the passkey must be available for Amazon::Credentials to decrypt the keys and thus it is stored with the credentials which is less than ideal. To avoid storing the passkey with the credentials, pass a reference to a subroutine that will provide the passkey for encryption and decryption. You can even use the same passkey generator that is used by Amazon::Credentials (create_passkey).

The point here is to avoid storing credentials in the same object as the credentials to minimize the likelihood of exposing your credentials or your methods for encryption in logs...better but not perfect. It's still possible to expose your passkey and your credentials if you are not careful.

use Amazon::Credentials qw{ create_passkey };

my $passkey = create_passkey();

my $credentials = Amazon::Credentials( passkey => sub { return $passkey } );

A more secure approach would be for your subroutine to retrieve a passkey from a source other than your own program and never store the passkey inside your program.

Using a Custom Cipher

As noted, the default Crypt::CBC cipher is used for encrypting your credentials, however you can pass a custom cipher supported by Crypt::CBC further obfuscating the methods used to encrypt your credentials.

my $credentials = Amazon::Credentials(
  passkey => \&fetch_passkey,
  cipher  => 'Blowfish'
);
Rotating Passkeys and Credentials

For those with the (justifiably) paranoid feeling that no matter what you do there are those determined to crack even encrypted or obfuscated credentials once exposed, you can periodically rotate the credentials.

If you are not using a custom passkey...

$credentials->rotate_credentials;

...or if you have a custom passkey generator your subroutine must continue to provide the old passkey before you can reset the passkey.

use Amazon::Credentials qw{ create_passkey };

my $passkey = create_passkey;

sub get_passkey {
  my ($regenerate) = shift;
  
  return $regenerate ? create_passkey : $passkey;
} 

my $credentials = Amazon::Credentials->new( passkey => \&get_passkey );

$passkey = $credentials->rotate_credentials(get_passkey(1));
Using Custom Encryption Methods

Finally, you can also provide your own encrypt() and decrypt() methods when you call the new() constructor. These methods will be passed the string to encrypt or decrypt and the passkey. Your methods should return the decrypted or encrypted strings. Your methods can ignore the passkey if your methods provide their own passkey or mechanisms for encryption.

use Amazon::Credentials qw( create_passkey };

my $passkey = create_passkey();

sub my_encrypt {
  my ($self, $str) = @_;

  ...
  return $encrypted_str;
}

sub my_decrypt {

  ...
  return $deecrypted_str;
}

my $creds = Amazon::Credentials->new( encrypt => \&my_encrypt,
                                      decrypt => \&my_decrypt,
                                      passkey => sub { return $passkey },
                                    );

Securing Your Logs

To troubleshoot potential bugs in this module or to understand what Amazon::Credentials is doing you can pass a debug flag that will write potentially helpful info to STDERR.

To prevent possible exposure of credentials in debug messages, the module will not write log messages that contain your credentials even if your debug flag is set to a true value. In order to debug output of all content you the insecure flag to any of the values shown below.

insecure = false (0, '', undef)

If the debug flag is true, any message that might potentially contain credentials is not written to STDERR. This is the default.

insecure = 1

Setting insecure to 1 will allow more debug messages, however credentials will be masked.

insecure = 2 or 'insecure'

This setting, along with setting the debug mode to a true value will enable full debugging.

Use Temporary Credentials

One additional tip to help prevent the use of your credentials even if they have been exposed in logs or files. Use temporary credentials with short expiration times whenever possible. Amazon::Credentials provides methods to determine if your credentials have expired and a method to refresh them when they have.

if ( $credentials->is_token_expired ) {
  $credentials->refresh_token;
}

Additonal Notes on Logging

Versions 1.0.18 and 1.0.19 allowed you to enable debugging by setting the environment variable DEBUG to any true value to enable basic debug output. Version 1.0.18 would log information to STDERR including payloads that might contain credentials. Version 1.0.19 would prevent writing any payload with credentials unless the debug mode was set to 2 or 'insecure'.

Starting with version 1.1.0 the Amazon::Credentials will not use the environment variable DEBUG to enable debugging. You must explicitly pass the debug flag in the constructor to enable debugging. Keep in mind however that you should avoid allowing upstream programs to use environment variables to set debugging modes that you might pass to Amazon::Credentials.

INCOMPATIBILITIES

This module has not been tested on Windows OS.

CONTRIBUTING

You can find this project on GitHub at https://github.com/rlauer6/perl-Amazon-Credentials. PRs are always welcomed!

LICENSE AND COPYRIGHT

This module is free software. It may be used, redistributed and/or modified under the same terms as Perl itself.

AUTHOR

Rob Lauer - <rlauer6@comcast.net>