/** Authentication helpers — each returns a function the connection calls
*  with `send(command)` and `recv()` and returns on success or throws on
*  an auth failure reply. Keeping them pure lets unit tests drive them
*  with fake send/recv. */
import type { SmtpReply } from "./reply.mjs";
export type { SmtpReply } from "./reply.mjs";
export type AuthMethod = "LOGIN" | "PLAIN" | "CRAM-MD5" | "XOAUTH2";
export interface AuthContext {
	send: (line: string) => Promise<void>;
	recv: () => Promise<SmtpReply>;
}
/** Pick the best advertised method given caller preference + capabilities.
*  Order reflects practical recommendations (Brevo/SendGrid/Mailgun docs): */
export declare function pickAuthMethod(advertised: ReadonlySet<string>, prefer?: AuthMethod | "AUTO"): AuthMethod | null;
export declare function authPlain(ctx: AuthContext, user: string, password: string): Promise<SmtpReply>;
export declare function authLogin(ctx: AuthContext, user: string, password: string): Promise<SmtpReply>;
export declare function authCramMd5(ctx: AuthContext, user: string, password: string, hmac: (key: string, data: string) => string): Promise<SmtpReply>;
export declare function authXoauth2(ctx: AuthContext, user: string, accessToken: string): Promise<SmtpReply>;