diff --git a/auth_options.go b/auth_options.go
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+++ b/auth_options.go
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+package gophercloud
+
+// AuthOptions lets anyone calling Authenticate() supply the required access credentials.
+// Its fields are the union of those recognized by each identity implementation and provider.
+type AuthOptions struct {
+
+	// IdentityEndpoint specifies the HTTP endpoint offering the Identity API of the appropriate version.
+	// Required by the identity services, but often populated by a provider Client.
+	IdentityEndpoint string
+
+	// Username is required if using Identity V2 API.
+	// Consult with your provider's control panel to discover your account's username.
+	// In Identity V3, either UserID or a combination of Username and DomainID or DomainName.
+	Username, UserID string
+
+	// Exactly one of Password or ApiKey is required for the Identity V2 and V3 APIs.
+	// Consult with your provider's control panel to discover your account's preferred method of authentication.
+	Password, APIKey string
+
+	// At most one of DomainID and DomainName must be provided if using Username with Identity V3.
+	// Otherwise, either are optional.
+	DomainID, DomainName string
+
+	// The TenantID and TenantName fields are optional for the Identity V2 API.
+	// Some providers allow you to specify a TenantName instead of the TenantId.
+	// Some require both.  Your provider's authentication policies will determine
+	// how these fields influence authentication.
+	TenantID, TenantName string
+
+	// AllowReauth should be set to true if you grant permission for Gophercloud to
+	// cache your credentials in memory, and to allow Gophercloud to attempt to
+	// re-authenticate automatically if/when your token expires.  If you set it to
+	// false, it will not cache these settings, but re-authentication will not be
+	// possible.  This setting defaults to false.
+	AllowReauth bool
+}