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README.md

@@ -24,3 +24,79 @@ sudo make install
 
   The name of the authorization scope that will appear in the error response.
 
+
+## Example: Postfix server (smtpd) / client (smtp) authentication configuration
+
+* `main.cf`:
+
+  ```
+# ... OTHER SETTINGS GO HERE ...
+
+# SERVER
+smtpd_sasl_auth_enable = yes
+smtpd_sasl_path = smtpd
+smtpd_relay_restrictions = permit_sasl_authenticated, reject
+
+# CLIENT
+relayhost = [smtp.gmail.com]:587
+smtp_sasl_auth_enable = yes
+smtp_sasl_password_maps = hash:/etc/postfix/saslpasswd
+smtp_sasl_mechanism_filter = xoauth2
+smtp_sasl_security_options =
+smtp_tls_security_level = may
+smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
+```
+
+* `/etc/postfix/saslpasswd`:
+
+  ```
+[smtp.gmail.com]:587    [email protected]:OAUTH2-TOKEN-RETRIEVED-BY-GMAIL-OAUTH2-TOOLS
+```
+
+  * `/etc/postfix/saslpasswd.db` needs to be generated with `postmap`:
+
+    ```
+# postmap /etc/postfix/saslpasswd
+```
+
+  * Gmail OAuth2 Tools can be found [here](https://github.com/google/gmail-oauth2-tools).
+
+* `/etc/postfix/tls_policy`:
+
+  ```
+[smtp.gmail.com]:587    encrypt
+```
+
+  * `/etc/postfix/tls_policy.db` needs to be generated with `postmap`:
+
+    ```
+# postmap /etc/postfix/tls_policy
+```
+
+* `${sasl_plugin_dir}/smtpd.conf`:
+
+  ```
+log_level: DEBUG
+sql_engine: sqlite3
+sql_database: /etc/sasldb2.sqlite3
+sql_select: SELECT props.value FROM users JOIN props ON users.id=props.user_id WHERE users.name='%u' AND users.realm='%r' AND props.name='%p'
+xoauth2_scope: https://mail.example.com/
+auxprop_plugin: sql
+mech_list: xoauth2
+```
+
+* `/etc/sasldb2.sqlite3`:
+
+  Generated from the following DDL and SQL statements:
+
+  ```
+PRAGMA foreign_keys=OFF;
+BEGIN TRANSACTION;
+CREATE TABLE users (id INTEGER PRIMARY KEY, name VARCHAR, password VARCHAR, realm VARCHAR);
+INSERT INTO "users" VALUES(1,'test','test','example.com');
+CREATE TABLE props (id INTEGER PRIMARY KEY, user_id INTEGER, name VARCHAR, value VARCHAR, FOREIGN KEY (user_id) REFERENCES users (id));
+INSERT INTO "props" VALUES(1,1,'test','test');
+INSERT INTO "props" VALUES(2,1,'userPassword','*');
+INSERT INTO "props" VALUES(3,1,'oauth2BearerTokens','token');
+COMMIT;
+```