[js][auth] update firebase.auth.EmailAuthProvider to support link credentials

lib/modules/auth/providers/EmailAuthProvider.js

@@ -4,7 +4,8 @@
  */
 import type { AuthCredential } from '../types';
 
-const providerId = 'password';
+const linkProviderId = 'emailLink';
+const passwordProviderId = 'password';
 
 export default class EmailAuthProvider {
   constructor() {
@@ -13,15 +14,37 @@ export default class EmailAuthProvider {
     );
   }
 
+  static get EMAIL_LINK_SIGN_IN_METHOD(): string {
+    return linkProviderId;
+  }
+
+  static get EMAIL_PASSWORD_SIGN_IN_METHOD(): string {
+    return passwordProviderId;
+  }
+
   static get PROVIDER_ID(): string {
-    return providerId;
+    return passwordProviderId;
   }
 
   static credential(email: string, password: string): AuthCredential {
     return {
       token: email,
       secret: password,
-      providerId,
+      providerId: passwordProviderId,
+    };
+  }
+
+  /**
+   * Initialize an EmailAuthProvider credential using an email and an email link after a sign in with email link operation.
+   * @param email Email address.
+   * @param emailLink Sign-in email link.
+   * @returns {{token: string, secret: string, providerId: string}}
+   */
+  static credentialWithLink(email: string, emailLink: string): AuthCredential {
+    return {
+      token: email,
+      secret: emailLink,
+      providerId: linkProviderId,
     };
   }
 }