diff --git a/authenticate.go b/authenticate.go
index 19fabf6..754823c 100644
--- a/authenticate.go
+++ b/authenticate.go
@@ -1,13 +1,17 @@
 package gophercloud
 
-import (
-	"fmt"
-)
-
 type AuthOptions struct {
 	Username, Password, TenantId string
 }
 
-func Authenticate(provider string, options AuthOptions) (*int, error) {
-	return nil, fmt.Errorf("Not implemented.")
+func (c *Context) Authenticate(provider string, options AuthOptions) (*int, error) {
+	_, err := c.ProviderByName(provider)
+	if err != nil {
+		return nil, err
+	}
+
+	if (options.Username == "") || (options.Password == "") {
+		return nil, ErrCredentials
+	}
+	return nil, nil
 }