Expose OAuth token provider for use outside autorest (#520)

* feat: extract token creation to public method for MSI auth

* Add getter for token provider on BearerAuthorizer

autorest/authorization.go

@@ -138,6 +138,11 @@ func (ba *BearerAuthorizer) WithAuthorization() PrepareDecorator {
 	}
 }
 
+// TokenProvider returns OAuthTokenProvider so that it can be used for authorization outside the REST.
+func (ba *BearerAuthorizer) TokenProvider() adal.OAuthTokenProvider {
+	return ba.tokenProvider
+}
+
 // BearerAuthorizerCallbackFunc is the authentication callback signature.
 type BearerAuthorizerCallbackFunc func(tenantID, resource string) (*BearerAuthorizer, error)
 

autorest/azure/auth/auth.go

@@ -713,8 +713,8 @@ type MSIConfig struct {
 	ClientID string
 }
 
-// Authorizer gets the authorizer from MSI.
-func (mc MSIConfig) Authorizer() (autorest.Authorizer, error) {
+// ServicePrincipalToken creates a ServicePrincipalToken from MSI.
+func (mc MSIConfig) ServicePrincipalToken() (*adal.ServicePrincipalToken, error) {
 	msiEndpoint, err := adal.GetMSIEndpoint()
 	if err != nil {
 		return nil, err
@@ -733,5 +733,15 @@ func (mc MSIConfig) Authorizer() (autorest.Authorizer, error) {
 		}
 	}
 
+	return spToken, nil
+}
+
+// Authorizer gets the authorizer from MSI.
+func (mc MSIConfig) Authorizer() (autorest.Authorizer, error) {
+	spToken, err := mc.ServicePrincipalToken()
+	if err != nil {
+		return nil, err
+	}
+
 	return autorest.NewBearerAuthorizer(spToken), nil
 }