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+// Package credentials provides credential retrieval and management
+//
+// The Credentials is the primary method of getting access to and managing
+// credentials Values. Using dependency injection retrieval of the credential
+// values is handled by a object which satisfies the Provider interface.
+//
+// By default the Credentials.Get() will cache the successful result of a
+// Provider's Retrieve() until Provider.IsExpired() returns true. At which
+// point Credentials will call Provider's Retrieve() to get new credential Value.
+//
+// The Provider is responsible for determining when credentials Value have expired.
+// It is also important to note that Credentials will always call Retrieve the
+// first time Credentials.Get() is called.
+//
+// Example of using the environment variable credentials.
+//
+// creds := NewEnvCredentials()
+//
+// // Retrieve the credentials value
+// credValue, err := creds.Get()
+// if err != nil {
+// // handle error
+// }
+//
+// Example of forcing credentials to expire and be refreshed on the next Get().
+// This may be helpful to proactively expire credentials and refresh them sooner
+// than they would naturally expire on their own.
+//
+// creds := NewCredentials(&EC2RoleProvider{})
+// creds.Expire()
+// credsValue, err := creds.Get()
+// // New credentials will be retrieved instead of from cache.
+//
+//
+// Custom Provider
+//
+// Each Provider built into this package also provides a helper method to generate
+// a Credentials pointer setup with the provider. To use a custom Provider just
+// create a type which satisfies the Provider interface and pass it to the
+// NewCredentials method.
+//
+// type MyProvider struct{}
+// func (m *MyProvider) Retrieve() (Value, error) {...}
+// func (m *MyProvider) IsExpired() bool {...}
+//
+// creds := NewCredentials(&MyProvider{})
+// credValue, err := creds.Get()
+//
+package credentials
+
+import (
+ "sync"
+ "time"
+)
+
+// AnonymousCredentials is an empty Credential object that can be used as
+// dummy placeholder credentials for requests that do not need signed.
+//
+// This Credentials can be used to configure a service to not sign requests
+// when making service API calls. For example, when accessing public
+// s3 buckets.
+//
+// svc := s3.New(&aws.Config{Credentials: AnonymousCredentials})
+// // Access public S3 buckets.
+//
+// @readonly
+var AnonymousCredentials = NewStaticCredentials("", "", "")
+
+// A Value is the AWS credentials value for individual credential fields.
+type Value struct {
+ // AWS Access key ID
+ AccessKeyID string
+
+ // AWS Secret Access Key
+ SecretAccessKey string
+
+ // AWS Session Token
+ SessionToken string
+
+ // Provider used to get credentials
+ ProviderName string
+}
+
+// A Provider is the interface for any component which will provide credentials
+// Value. A provider is required to manage its own Expired state, and what to
+// be expired means.
+//
+// The Provider should not need to implement its own mutexes, because
+// that will be managed by Credentials.
+type Provider interface {
+ // Refresh returns nil if it successfully retrieved the value.
+ // Error is returned if the value were not obtainable, or empty.
+ Retrieve() (Value, error)
+
+ // IsExpired returns if the credentials are no longer valid, and need
+ // to be retrieved.
+ IsExpired() bool
+}
+
+// A Expiry provides shared expiration logic to be used by credentials
+// providers to implement expiry functionality.
+//
+// The best method to use this struct is as an anonymous field within the
+// provider's struct.
+//
+// Example:
+// type EC2RoleProvider struct {
+// Expiry
+// ...
+// }
+type Expiry struct {
+ // The date/time when to expire on
+ expiration time.Time
+
+ // If set will be used by IsExpired to determine the current time.
+ // Defaults to time.Now if CurrentTime is not set. Available for testing
+ // to be able to mock out the current time.
+ CurrentTime func() time.Time
+}
+
+// SetExpiration sets the expiration IsExpired will check when called.
+//
+// If window is greater than 0 the expiration time will be reduced by the
+// window value.
+//
+// Using a window is helpful to trigger credentials to expire sooner than
+// the expiration time given to ensure no requests are made with expired
+// tokens.
+func (e *Expiry) SetExpiration(expiration time.Time, window time.Duration) {
+ e.expiration = expiration
+ if window > 0 {
+ e.expiration = e.expiration.Add(-window)
+ }
+}
+
+// IsExpired returns if the credentials are expired.
+func (e *Expiry) IsExpired() bool {
+ if e.CurrentTime == nil {
+ e.CurrentTime = time.Now
+ }
+ return e.expiration.Before(e.CurrentTime())
+}
+
+// A Credentials provides synchronous safe retrieval of AWS credentials Value.
+// Credentials will cache the credentials value until they expire. Once the value
+// expires the next Get will attempt to retrieve valid credentials.
+//
+// Credentials is safe to use across multiple goroutines and will manage the
+// synchronous state so the Providers do not need to implement their own
+// synchronization.
+//
+// The first Credentials.Get() will always call Provider.Retrieve() to get the
+// first instance of the credentials Value. All calls to Get() after that
+// will return the cached credentials Value until IsExpired() returns true.
+type Credentials struct {
+ creds Value
+ forceRefresh bool
+ m sync.Mutex
+
+ provider Provider
+}
+
+// NewCredentials returns a pointer to a new Credentials with the provider set.
+func NewCredentials(provider Provider) *Credentials {
+ return &Credentials{
+ provider: provider,
+ forceRefresh: true,
+ }
+}
+
+// Get returns the credentials value, or error if the credentials Value failed
+// to be retrieved.
+//
+// Will return the cached credentials Value if it has not expired. If the
+// credentials Value has expired the Provider's Retrieve() will be called
+// to refresh the credentials.
+//
+// If Credentials.Expire() was called the credentials Value will be force
+// expired, and the next call to Get() will cause them to be refreshed.
+func (c *Credentials) Get() (Value, error) {
+ c.m.Lock()
+ defer c.m.Unlock()
+
+ if c.isExpired() {
+ creds, err := c.provider.Retrieve()
+ if err != nil {
+ return Value{}, err
+ }
+ c.creds = creds
+ c.forceRefresh = false
+ }
+
+ return c.creds, nil
+}
+
+// Expire expires the credentials and forces them to be retrieved on the
+// next call to Get().
+//
+// This will override the Provider's expired state, and force Credentials
+// to call the Provider's Retrieve().
+func (c *Credentials) Expire() {
+ c.m.Lock()
+ defer c.m.Unlock()
+
+ c.forceRefresh = true
+}
+
+// IsExpired returns if the credentials are no longer valid, and need
+// to be retrieved.
+//
+// If the Credentials were forced to be expired with Expire() this will
+// reflect that override.
+func (c *Credentials) IsExpired() bool {
+ c.m.Lock()
+ defer c.m.Unlock()
+
+ return c.isExpired()
+}
+
+// isExpired helper method wrapping the definition of expired credentials.
+func (c *Credentials) isExpired() bool {
+ return c.forceRefresh || c.provider.IsExpired()
+}