Added users sessions (#696)

Added login/logout pages and respective database methods for handling users sessions.

internal/data/session/session_postgres.go

@@ -0,0 +1,89 @@
+package session
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"github.com/jackc/pgx/v4/pgxpool"
+	"micromdm.io/v2/pkg/viewer"
+)
+
+// Postgres provides methods for creating sessions in PostgreSQL.
+type Postgres struct{ db *pgxpool.Pool }
+
+// NewPostgres creates a Postgres client.
+func NewPostgres(db *pgxpool.Pool) *Postgres {
+	return &Postgres{db: db}
+}
+
+func (d *Postgres) CreateSession(ctx context.Context) (*Session, error) {
+	s, err := create(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	q := `INSERT INTO sessions ( id, user_id ) VALUES ( $1, $2 ) RETURNING "created_at", "accessed_at";`
+	if err := d.db.QueryRow(ctx, q,
+		s.ID,
+		s.UserID,
+	).Scan(&s.CreatedAt, &s.AccessedAt); err != nil {
+		return nil, fmt.Errorf("store new session in postgres: %w", err)
+	}
+
+	return s, nil
+}
+
+func (d *Postgres) DestroySession(ctx context.Context) error {
+	v, ok := viewer.FromContext(ctx)
+	if !ok || v.SessionID == "" {
+		return fmt.Errorf("session: missing valid viewer %v", v)
+	}
+
+	q := `DELETE FROM sessions WHERE id = $1;`
+
+	if _, err := d.db.Exec(ctx, q, v.SessionID); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (d *Postgres) FindSession(ctx context.Context, id string) (*Session, error) {
+	q := fmt.Sprintf(`WITH updated AS (
+  UPDATE sessions SET accessed_at = now() at time zone 'utc'
+  FROM (
+    SELECT user_id FROM sessions
+    WHERE id = $1
+    LIMIT 1
+    ) sub
+    JOIN users u on u.id = sub.user_id
+    WHERE sessions.id = $2
+    RETURNING %s
+  )
+	SELECT %s from updated;`, // TODO: add username, full_name to session struct.
+		strings.Join(prefixTable("sessions", columns()), `, `),
+		strings.Join(columns(), `, `),
+	)
+
+	s := &Session{ID: id}
+	if err := d.db.QueryRow(ctx, q, id, id).Scan(
+		&s.ID,
+		&s.UserID,
+		&s.CreatedAt,
+		&s.AccessedAt,
+	); err != nil {
+		return nil, err
+	}
+
+	return s, nil
+
+}
+
+func prefixTable(prefix string, ss []string) []string {
+	result := make([]string, len(ss), cap(ss))
+	for i, s := range ss {
+		result[i] = fmt.Sprintf("%s.%s", prefix, s)
+	}
+	return result
+}