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provider.go
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provider.go
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// +build go1.8
// Package plugincreds implements a credentials provider sourced from a Go
// plugin. This package allows you to use a Go plugin to retrieve AWS credentials
// for the SDK to use for service API calls.
//
// As of Go 1.8 plugins are only supported on the Linux platform.
//
// Plugin Symbol Name
//
// The "GetAWSSDKCredentialProvider" is the symbol name that will be used to
// lookup the credentials provider getter from the plugin. If you want to use a
// custom symbol name you should use GetPluginProviderFnsByName to lookup the
// symbol by a custom name.
//
// This symbol is a function that returns two additional functions. One to
// retrieve the credentials, and another to determine if the credentials have
// expired.
//
// Plugin Symbol Signature
//
// The plugin credential provider requires the symbol to match the
// following signature.
//
// func() (RetrieveFn func() (key, secret, token string, err error), IsExpiredFn func() bool)
//
// Plugin Implementation Exmaple
//
// The following is an example implementation of a SDK credential provider using
// the plugin provider in this package. See the SDK's example/aws/credential/plugincreds/plugin
// folder for a runnable example of this.
//
// package main
//
// func main() {}
//
// var myCredProvider provider
//
// // Build: go build -o plugin.so -buildmode=plugin plugin.go
// func init() {
// // Initialize a mock credential provider with stubs
// myCredProvider = provider{"a","b","c"}
// }
//
// // GetAWSSDKCredentialProvider is the symbol SDK will lookup and use to
// // get the credential provider's retrieve and isExpired functions.
// func GetAWSSDKCredentialProvider() (func() (key, secret, token string, err error), func() bool) {
// return myCredProvider.Retrieve, myCredProvider.IsExpired
// }
//
// // mock implementation of a type that returns retrieves credentials and
// // returns if they have expired.
// type provider struct {
// key, secret, token string
// }
//
// func (p provider) Retrieve() (key, secret, token string, err error) {
// return p.key, p.secret, p.token, nil
// }
//
// func (p *provider) IsExpired() bool {
// return false;
// }
//
// Configuring SDK for Plugin Credentials
//
// To configure the SDK to use a plugin's credential provider you'll need to first
// open the plugin file using the plugin standard library package. Once you have
// a handle to the plugin you can use the NewCredentials function of this package
// to create a new credentials.Credentials value that can be set as the
// credentials loader of a Session or Config. See the SDK's example/aws/credential/plugincreds
// folder for a runnable example of this.
//
// // Open plugin, and load it into the process.
// p, err := plugin.Open("somefile.so")
// if err != nil {
// return nil, err
// }
//
// // Create a new Credentials value which will source the provider's Retrieve
// // and IsExpired functions from the plugin.
// creds, err := plugincreds.NewCredentials(p)
// if err != nil {
// return nil, err
// }
//
// // Example to configure a Session with the newly created credentials that
// // will be sourced using the plugin's functionality.
// sess := session.Must(session.NewSession(&aws.Config{
// Credentials: creds,
// }))
package plugincreds
import (
"fmt"
"plugin"
"github.com/aws/aws-sdk-go/aws/awserr"
"github.com/aws/aws-sdk-go/aws/credentials"
)
// ProviderSymbolName the symbol name the SDK will use to lookup the plugin
// provider value from.
const ProviderSymbolName = `GetAWSSDKCredentialProvider`
// ProviderName is the name this credentials provider will label any returned
// credentials Value with.
const ProviderName = `PluginCredentialsProvider`
const (
// ErrCodeLookupSymbolError failed to lookup symbol
ErrCodeLookupSymbolError = "LookupSymbolError"
// ErrCodeInvalidSymbolError symbol invalid
ErrCodeInvalidSymbolError = "InvalidSymbolError"
// ErrCodePluginRetrieveNil Retrieve function was nil
ErrCodePluginRetrieveNil = "PluginRetrieveNilError"
// ErrCodePluginIsExpiredNil IsExpired Function was nil
ErrCodePluginIsExpiredNil = "PluginIsExpiredNilError"
// ErrCodePluginProviderRetrieve plugin provider's retrieve returned error
ErrCodePluginProviderRetrieve = "PluginProviderRetrieveError"
)
// Provider is the credentials provider that will use the plugin provided
// Retrieve and IsExpired functions to retrieve credentials.
type Provider struct {
RetrieveFn func() (key, secret, token string, err error)
IsExpiredFn func() bool
}
// NewCredentials returns a new Credentials loader using the plugin provider.
// If the symbol isn't found or is invalid in the plugin an error will be
// returned.
func NewCredentials(p *plugin.Plugin) (*credentials.Credentials, error) {
retrieve, isExpired, err := GetPluginProviderFns(p)
if err != nil {
return nil, err
}
return credentials.NewCredentials(Provider{
RetrieveFn: retrieve,
IsExpiredFn: isExpired,
}), nil
}
// Retrieve will return the credentials Value if they were successfully retrieved
// from the underlying plugin provider. An error will be returned otherwise.
func (p Provider) Retrieve() (credentials.Value, error) {
creds := credentials.Value{
ProviderName: ProviderName,
}
k, s, t, err := p.RetrieveFn()
if err != nil {
return creds, awserr.New(ErrCodePluginProviderRetrieve,
"failed to retrieve credentials with plugin provider", err)
}
creds.AccessKeyID = k
creds.SecretAccessKey = s
creds.SessionToken = t
return creds, nil
}
// IsExpired will return the expired state of the underlying plugin provider.
func (p Provider) IsExpired() bool {
return p.IsExpiredFn()
}
// GetPluginProviderFns returns the plugin's Retrieve and IsExpired functions
// returned by the plugin's credential provider getter.
//
// Uses ProviderSymbolName as the symbol name when lookup up the symbol. If you
// want to use a different symbol name, use GetPluginProviderFnsByName.
func GetPluginProviderFns(p *plugin.Plugin) (func() (key, secret, token string, err error), func() bool, error) {
return GetPluginProviderFnsByName(p, ProviderSymbolName)
}
// GetPluginProviderFnsByName returns the plugin's Retrieve and IsExpired functions
// returned by the plugin's credential provider getter.
//
// Same as GetPluginProviderFns, but takes a custom symbolName to lookup with.
func GetPluginProviderFnsByName(p *plugin.Plugin, symbolName string) (func() (key, secret, token string, err error), func() bool, error) {
sym, err := p.Lookup(symbolName)
if err != nil {
return nil, nil, awserr.New(ErrCodeLookupSymbolError,
fmt.Sprintf("failed to lookup %s plugin provider symbol", symbolName), err)
}
fn, ok := sym.(func() (func() (key, secret, token string, err error), func() bool))
if !ok {
return nil, nil, awserr.New(ErrCodeInvalidSymbolError,
fmt.Sprintf("symbol %T, does not match the 'func() (func() (key, secret, token string, err error), func() bool)' type", sym), nil)
}
retrieveFn, isExpiredFn := fn()
if retrieveFn == nil {
return nil, nil, awserr.New(ErrCodePluginRetrieveNil,
"the plugin provider retrieve function cannot be nil", nil)
}
if isExpiredFn == nil {
return nil, nil, awserr.New(ErrCodePluginIsExpiredNil,
"the plugin provider isExpired function cannot be nil", nil)
}
return retrieveFn, isExpiredFn, nil
}