Add chain provider

Signed-off-by: Pierre-Emmanuel Jacquier <15922119+pierre-emmanuelJ@users.noreply.github.com>

v3/credentials/chain.go

@@ -0,0 +1,57 @@
+package credentials
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrNoValidCredentialProviders = errors.New("no valid credential providers")
+)
+
+// A ChainProvider will search for a provider which returns credentials
+// and cache that provider until Retrieve is called again.
+type ChainProvider struct {
+	Providers []Provider
+	current   Provider
+}
+
+// NewChainCredentials returns a pointer to a new Credentials object
+// wrapping a chain of providers.
+func NewChainCredentials(providers []Provider) *Credentials {
+	return NewCredentials(&ChainProvider{
+		Providers: append([]Provider{}, providers...),
+	})
+}
+
+// Retrieve returns the credentials value or error if no provider returned
+// without error.
+//
+// If a provider is found it will be cached and any calls to IsExpired()
+// will return the expired state of the cached provider.
+func (c *ChainProvider) Retrieve() (Value, error) {
+	var errs = ErrNoValidCredentialProviders
+
+	for _, p := range c.Providers {
+		creds, err := p.Retrieve()
+		if err == nil {
+			c.current = p
+			return creds, nil
+		}
+
+		errs = fmt.Errorf("%v: %w", errs, err)
+	}
+	c.current = nil
+
+	return Value{}, fmt.Errorf("chain provider: %w", errs)
+}
+
+// IsExpired will returned the expired state of the currently cached provider
+// if there is one.  If there is no current provider, true will be returned.
+func (c *ChainProvider) IsExpired() bool {
+	if c.current != nil {
+		return c.current.IsExpired()
+	}
+
+	return true
+}