Change:
This looks a lot worse than it really is. Reflowing text causes massive diffs, which github somehow manages to make look like entirely new text.

Discussion:
Abstract An application server can use the method described to voluntarily <del> identify itself to a push service.  This identification information can be used by the push service to attribute requests that are made by the same application server to a single entity.  An application server can include additional information that the operator of a push service can use to contact the operator of the application server. This identification information can be used to restrict the use of a push subscription to a single application server. </del> <ins> identify itself to a push service.  The "vapid" authentication scheme allows a client to include its an identity in a signed token with requests that it makes.  The signature can be used by the push service to attribute requests that are made by the same application server to a single entity.  The identification information can allow the operator of a push service to contact the operator of the application server.  The signature can be used to restrict the use of a push subscription to a single application server. </ins> 1.

the protocol provides.  For these reasons, RFC8030 does not define a mandatory system for authentication of application servers. <del> An unfortunate consequence of this design is that a push service is exposed to a greater risk of denial of service attack.  While requests from application servers can be indirectly attributed to user agents, this is not always efficient or even sufficient. </del> <ins> An unfortunate consequence of the design of RFC8030 is that a push service is exposed to a greater risk of denial of service attack. While requests from application servers can be indirectly attributed to user agents, this is not always efficient or even sufficient. </ins> Providing more information about the application server directly to a push service allows the push service to better distinguish between legitimate and bogus requests.

This JWT is included in an Authorization header field, using an auth- scheme of "vapid".  A push service MAY reject a request with a 403 (Forbidden) status code RFC7235 if the JWT signature or its claims <del> are invalid. </del> <ins> are invalid.  A push service MUST NOT use information from an invalid token. </ins> The JWT MUST use a JSON Web Signature (JWS) RFC7515.  The signature MUST use ECDSA on the NIST P-256 curve FIPS186 which is identified as

this authentication scheme. This authentication scheme is intended for use by an application <del> server when using the Web Push protocol RFC8030, but it could be used in other contexts if applicable. </del> <ins> server when using the Web Push protocol RFC8030. </ins> 3.1.

sources.  Secondarily, the X9.62 encoding is also considerably smaller. <del> Some implementations permit the same P-256 key to be used for signing and key exchange.  An application server MUST select a different private key for the key exchange I-D.ietf-webpush-encryption and </del> <ins> Some elliptic curve implementations permit the same P-256 key to be used for signing and key exchange.  An application server MUST select a different private key for the key exchange WEBPUSH-ENCRYPTION and </ins> signing the authentication token.  Though a push service is not obligated to check either parameter for every push message, a push service SHOULD reject push messages that have identical values for

4.1. <del> The user agent includes the public key of the application server when requesting the creation of a push subscription.  This restricts use of the resulting subscription to application servers that are able to provide proof of possession for the corresponding private key. The public key is then added to the request to create a push subscription.  The push subscription request is extended to include a body.  The body of the request is a JSON object as described in RFC7159.  A "vapid" member is added to this JSON object, containing the public key on the P-256 curve, encoded in the uncompressed form X9.62 and base64url encoded RFC7515.  The media type of the body is set to "application/webpush-options+json" (see mime for registration of this media type). A push service MUST ignore the body of a request that uses a different media type.  For the "application/webpush-options+json" media type, a push service MUST ignore any members on this object that it does not understand. </del> <ins> A user agent that wishes to create a restricted subscription includes the public key of the application server when requesting the creation of a push subscription.  This restricts use of the resulting subscription to application servers that are able to provide proof of possession for the corresponding private key. The user agent then adds the public key to the request to create a push subscription.  The push subscription request is extended to include a body.  The body of the request is a JSON object as described in RFC7159.  The user agent adds a "vapid" member to this JSON object that contains a public key on the P-256 curve, encoded in the uncompressed form X9.62 and base64url encoded RFC7515.  The media type of the body is set to "application/webpush-options+json" (see mime for registration of this media type). A push service can ignore the body of a request to create a subscription that uses a different media type.  For the "application/ webpush-options+json" media type, a push service MUST ignore any members on this object that it does not understand. </ins> The example in ex-restrict shows a restriction to the key used in ex- push.  Extra whitespace is added to meet formatting constraints.

possession for the associated private key that was used when creating the push subscription. <del> A push service MUST reject a message that omits mandatory credentials with a 401 (Unauthorized) status code.  A push service MAY reject a message that includes invalid credentials with a 403 (Forbidden) status code.  Credentials are invalid if: </del> <ins> A push service MUST reject a message sent to a restricted push subscription if that message includes no "vapid" authentication or invalid "vapid" authentication.  A 401 (Unauthorized) status code might be used if the authentication is absent; a 403 (Forbidden) status code might be used if authentication is invalid. "vapid" authentication is invalid if: </ins> either the authentication token or public key are not included in the request,