[feature] Push notifications (#3587)

* Update push subscription API model to be Mastodon 4.0 compatible

* Add webpush-go dependency

# Conflicts:
#	go.sum

* Single-row table for storing instance's VAPID key pair

* Generate VAPID key pair during startup

* Add VAPID public key to instance info API

* Return VAPID public key when registering an app

* Store Web Push subscriptions in DB

* Add Web Push sender (similar to email sender)

* Add no-op push senders to most processor tests

* Test Web Push notifications from workers

* Delete Web Push subscriptions when account is deleted

* Implement push subscription API

* Linter fixes

* Update Swagger

* Fix enum to int migration

* Fix GetVAPIDKeyPair

* Create web push subscriptions table with indexes

* Log Web Push server error messages

* Send instance URL as Web Push JWT subject

* Accept any 2xx code as a success

* Fix malformed VAPID sub claim

* Use packed notification flags

* Remove unused date columns

* Add notification type for update notifications

Not used yet

* Make GetVAPIDKeyPair idempotent

and remove PutVAPIDKeyPair

* Post-rebase fixes

* go mod tidy

* Special-case 400 errors other than 408/429

Most client errors should remove the subscription.

* Improve titles, trim body to reasonable length

* Disallow cleartext HTTP for Web Push servers

* Fix lint

* Remove redundant index on unique column

Also removes redundant unique and notnull tags on ID column since these are implied by pk

* Make realsender.go more readable

* Use Tobi's style for wrapping errors

* Restore treating all 5xx codes as temporary problems

* Always load target account settings

* Stub `policy` and `standard`

* webpush.Sender: take type converter as ctor param

* Move webpush.MockSender and noopSender into testrig

vendor/github.com/SherClockHolmes/webpush-go/vapid.go

@@ -0,0 +1,117 @@
+package webpush
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"math/big"
+	"net/url"
+	"time"
+
+	"github.com/golang-jwt/jwt"
+)
+
+// GenerateVAPIDKeys will create a private and public VAPID key pair
+func GenerateVAPIDKeys() (privateKey, publicKey string, err error) {
+	// Get the private key from the P256 curve
+	curve := elliptic.P256()
+
+	private, x, y, err := elliptic.GenerateKey(curve, rand.Reader)
+	if err != nil {
+		return
+	}
+
+	public := elliptic.Marshal(curve, x, y)
+
+	// Convert to base64
+	publicKey = base64.RawURLEncoding.EncodeToString(public)
+	privateKey = base64.RawURLEncoding.EncodeToString(private)
+
+	return
+}
+
+// Generates the ECDSA public and private keys for the JWT encryption
+func generateVAPIDHeaderKeys(privateKey []byte) *ecdsa.PrivateKey {
+	// Public key
+	curve := elliptic.P256()
+	px, py := curve.ScalarMult(
+		curve.Params().Gx,
+		curve.Params().Gy,
+		privateKey,
+	)
+
+	pubKey := ecdsa.PublicKey{
+		Curve: curve,
+		X:     px,
+		Y:     py,
+	}
+
+	// Private key
+	d := &big.Int{}
+	d.SetBytes(privateKey)
+
+	return &ecdsa.PrivateKey{
+		PublicKey: pubKey,
+		D:         d,
+	}
+}
+
+// getVAPIDAuthorizationHeader
+func getVAPIDAuthorizationHeader(
+	endpoint,
+	subscriber,
+	vapidPublicKey,
+	vapidPrivateKey string,
+	expiration time.Time,
+) (string, error) {
+	// Create the JWT token
+	subURL, err := url.Parse(endpoint)
+	if err != nil {
+		return "", err
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodES256, jwt.MapClaims{
+		"aud": fmt.Sprintf("%s://%s", subURL.Scheme, subURL.Host),
+		"exp": expiration.Unix(),
+		"sub": fmt.Sprintf("mailto:%s", subscriber),
+	})
+
+	// Decode the VAPID private key
+	decodedVapidPrivateKey, err := decodeVapidKey(vapidPrivateKey)
+	if err != nil {
+		return "", err
+	}
+
+	privKey := generateVAPIDHeaderKeys(decodedVapidPrivateKey)
+
+	// Sign token with private key
+	jwtString, err := token.SignedString(privKey)
+	if err != nil {
+		return "", err
+	}
+
+	// Decode the VAPID public key
+	pubKey, err := decodeVapidKey(vapidPublicKey)
+	if err != nil {
+		return "", err
+	}
+
+	return fmt.Sprintf(
+		"vapid t=%s, k=%s",
+		jwtString,
+		base64.RawURLEncoding.EncodeToString(pubKey),
+	), nil
+}
+
+// Need to decode the vapid private key in multiple base64 formats
+// Solution from: https://github.com/SherClockHolmes/webpush-go/issues/29
+func decodeVapidKey(key string) ([]byte, error) {
+	bytes, err := base64.URLEncoding.DecodeString(key)
+	if err == nil {
+		return bytes, nil
+	}
+
+	return base64.RawURLEncoding.DecodeString(key)
+}