[CMCSMACD-4695] Add a function for syncing users and roles (#10)

This will be used instead of migrations for making sure that a
database has the right users and roles.

Author: hundt-corbalt

migrations/user.go

@@ -0,0 +1,126 @@
+package migrations
+
+import (
+	"database/sql"
+	"fmt"
+	"log"
+
+	"github.com/jmoiron/sqlx"
+	"github.com/lib/pq"
+)
+
+type PostgreSQLUser struct {
+	Username   string
+	GrantRoles []string
+}
+
+type UserAuthenticationType string
+
+const (
+	UserAuthenticationTypeIAM      UserAuthenticationType = "iam"
+	UserAuthenticationTypePassword UserAuthenticationType = "password"
+)
+
+// Make sure that the given users exist in database cluster and have only the
+// role memberships specified. If authType is UserAuthenticationTypePassword,
+// set each user's password to its username. Otherwise remove each user's password
+// and also add the rds_iam role for each user.
+// All operations are done in a single transaction.
+func EnsureUsersWithRoles(db *sqlx.DB, users []PostgreSQLUser, authType UserAuthenticationType) error {
+	tx, err := db.Begin()
+	if err != nil {
+		return fmt.Errorf("Error starting transaction: %w", err)
+	}
+	defer func() {
+		err := tx.Rollback()
+		if err != nil && err != sql.ErrTxDone {
+			log.Printf("Error rolling back: %s", err)
+		}
+	}()
+
+	for _, user := range users {
+		createUserSQL := fmt.Sprintf(`
+			DO $$
+			DECLARE
+				username text := %s;
+			BEGIN
+				IF NOT EXISTS (
+					SELECT FROM pg_catalog.pg_user WHERE usename = username
+				) THEN
+					EXECUTE format('CREATE USER %%I', username);
+				END IF;
+			END
+			$$`, pq.QuoteLiteral(user.Username))
+		_, err := tx.Exec(createUserSQL)
+		if err != nil {
+			return fmt.Errorf("Failed to create user %q: %w", user.Username, err)
+		}
+
+		// Drop all existing roles
+		dropRolesSQL := fmt.Sprintf(`
+			DO $$
+			DECLARE
+				r RECORD;
+			BEGIN
+				FOR r IN
+					SELECT roleid::regrole AS granted_role
+					FROM pg_catalog.pg_auth_members
+					WHERE member = %s::regrole
+				LOOP
+					EXECUTE format('REVOKE %%I FROM %s', r.granted_role);
+				END LOOP;
+			END
+			$$;`, pq.QuoteLiteral(user.Username), pq.QuoteIdentifier(user.Username))
+		_, err = tx.Exec(dropRolesSQL)
+		if err != nil {
+			return fmt.Errorf("Failed to drop roles for user %q: %w", user.Username, err)
+		}
+
+		// There could be privileges on a variety of different objects.
+		// See https://www.postgresql.org/docs/current/sql-revoke.html
+		// But we will just worry about roles.
+
+		// Add roles
+		roles := user.GrantRoles
+		if authType == UserAuthenticationTypeIAM {
+			roles = append(roles, "rds_iam")
+		}
+		for _, role := range roles {
+			grantSQL := fmt.Sprintf("GRANT %s TO %s", pq.QuoteIdentifier(role), pq.QuoteIdentifier(user.Username))
+			_, err = tx.Exec(grantSQL)
+			if err != nil {
+				return fmt.Errorf("Failed to give role %q to user %q: %w", role, user.Username, err)
+			}
+		}
+
+		// Set or remove password
+		switch authType {
+		case UserAuthenticationTypePassword:
+			_, err = tx.Exec(
+				fmt.Sprintf("ALTER USER %s WITH PASSWORD %s",
+					pq.QuoteIdentifier(user.Username),
+					pq.QuoteLiteral(user.Username)),
+			)
+			if err != nil {
+				return fmt.Errorf("Failed to set password for user %q: %w", user.Username, err)
+			}
+		case UserAuthenticationTypeIAM:
+			_, err = tx.Exec(
+				fmt.Sprintf("ALTER USER %s WITH PASSWORD NULL",
+					pq.QuoteIdentifier(user.Username)),
+			)
+			if err != nil {
+				return fmt.Errorf("Failed to remove password for user %q: %w", user.Username, err)
+			}
+		default:
+			return fmt.Errorf("Invalid authType %q", authType)
+		}
+	}
+
+	err = tx.Commit()
+	if err != nil {
+		return fmt.Errorf("Error committing transaction: %w", err)
+	}
+
+	return nil
+}