Enable Email as a MFA method/option (#68)

This adds Email as a multi-factor authentication method/option. It reuses the `VerificationCode` for the code generation and validation.

It also refactors the email templating for easier repurposing.

Finally, it has a small Deno version bump.

Closes #25

lib/models/multi-factor-auth/email.ts

@@ -0,0 +1,50 @@
+import { MultiFactorAuthMethod, User } from '/lib/types.ts';
+import { MultiFactorAuthSetup } from '/lib/models/multi-factor-auth.ts';
+import { VerificationCodeModel } from '/lib/models/user.ts';
+import { EmailModel as EmailTransportModel } from '/lib/models/email.ts';
+
+export class EmailModel {
+  static async createMethod(
+    id: string,
+    name: string,
+    user: User,
+  ): Promise<MultiFactorAuthSetup> {
+    const method: MultiFactorAuthMethod = {
+      type: 'email',
+      id,
+      name,
+      enabled: false,
+      created_at: new Date(),
+      metadata: {},
+    };
+
+    await this.createAndSendCode(id, user);
+
+    return {
+      method,
+    };
+  }
+
+  static async createAndSendCode(
+    id: string,
+    user: User,
+  ): Promise<void> {
+    const code = await VerificationCodeModel.create(user, `${user.email}-${id}`, 'email');
+
+    await EmailTransportModel.sendLoginVerificationEmail(user.email, code);
+  }
+
+  static async verifyCode(
+    methodId: string,
+    code: string,
+    user: User,
+  ): Promise<boolean> {
+    try {
+      await VerificationCodeModel.validate(user, `${user.email}-${methodId}`, code, 'email');
+
+      return true;
+    } catch {
+      return false;
+    }
+  }
+}