While the primary benefit of Named Credentials is to allow the Salesforce platform to manage authentication transparently, there are scenarios dictated by "technical constraints" where this is not possible. If an external system uses a non-standard authentication protocol (e.g., a custom signing scheme), an architect can configure a Named Credential without a specified authentication protocol. In this specific case, the developer is responsible for constructing the necessary authentication headers (e.g., a custom Authorization header) within the Apex code that performs the callout. The Named Credential still provides the benefit of a managed endpoint URL and credential storage, but the authentication logic itself is handled in the code.

1. Salesforce Apex Developer Guide

"Named Credentials as Callout Endpoints": This guide explains the primary function of Named Credentials and also details the specific scenario for custom authentication. It states

"To handle the authentication in Apex

use a custom header. Create the named credential with no authentication protocol selected. Then in your Apex code

create the custom header for authentication and add it to the callout request." This directly supports option B as the correct method when technical constraints require it.

2. Salesforce Help

"Create a Custom Authentication Provider": This document outlines when custom authentication is needed. It mentions

"For an authentication protocol that is not OAuth 2.0

you can specify the named credential as the callout endpoint and handle the authentication in your code." This reinforces that handling authentication in code is the correct procedure for non-standard protocols.

3. Salesforce Help

"Login Flows": The official documentation describes Login Flows as a tool to "customize the login experience and integrate business processes with Salesforce authentication." Its purpose is for authenticating users into Salesforce

which is distinct from authenticating Salesforce to an external service

making option A incorrect.