TS_Proto/backend/internal/auth/auth.go

// Package auth carries the authenticated caller through the request context.
//
// Every tenant-scoped query in this service takes its tenant id from the
// Identity stored here, never from anything the client can name directly in a
// query string or body. That is the single rule that keeps tenants isolated.
package auth

import (
	"context"
	"errors"

	"github.com/travelswitch/travelhub/backend/internal/models"
)

// Identity is the authenticated user together with the tenant they signed into.
type Identity struct {
	User   models.User
	Tenant models.Tenant
}

// contextKey is unexported so no other package can collide with our key.
type contextKey struct{}

var identityKey contextKey

// ErrNoIdentity means the handler ran without authentication middleware in
// front of it, which is a programming error rather than a client error.
var ErrNoIdentity = errors.New("no identity in request context")

// WithIdentity returns a context carrying the identity.
func WithIdentity(ctx context.Context, id Identity) context.Context {
	return context.WithValue(ctx, identityKey, id)
}

// FromContext retrieves the identity placed by the auth middleware.
func FromContext(ctx context.Context) (Identity, error) {
	id, ok := ctx.Value(identityKey).(Identity)
	if !ok {
		return Identity{}, ErrNoIdentity
	}
	return id, nil
}

// IsAdmin reports whether the caller holds the tenant admin role.
func (i Identity) IsAdmin() bool {
	return i.User.Role == "admin"
}