Read

Purpose: Get one or more values addressed by the given path.

The client MAY have to obtain an authorization token before being able to access the values. If the server is able to satisfy the request it MUST return a success response. If the server is unable to fulfil the request, then the server MUST return an error response.

Arguments, of which path is mandatory:

• path The path as defined in VSS to one or more nodes in the VSS tree.
• filter Additional information defining the requested data.
• authorization The authorization token.

Success response:

• data The data structure contains one or more sets of a path and a data point structure.
• path The path for the associated data point structure.
• data point A structure containing one or more tuplets of value and timestamp.
• value The latest available value. Please note that also for actuators this returns the current value, and not a target value that might have been set.
• timestamp The capture time of the value.
• timestamp The time of the server request execution.

Update

Purpose: Provide altered value to the vehicle signal(s) addressed by the path

The client MAY have to obtain an authorization token before being able to update the vehicle signal(s). If the server is able to satisfy the request it MUST return a success response, else it MUST return an error response. Only actuator type signals can be updated. Please note that a success response does not guarantee that the actuation attempt to change to the updated target value has, or will, succeed. A client may monitor the actuation progress through subsequent reads of the actuator value.

Arguments, of which path and value are mandatory:

• path The path as defined in VSS to a single node in the VSS tree.
• value The value by which the vehicle signal addressed by the path will be updated to.
• authorization The authorization token.

Success response:

• timestamp The time of the server request execution. This may not be the same as the final update time of the signal.

Subscribe

Purpose: Get asynchronous messages containing the value(s) addressed by the path. The triggering rules for issuing the notification messages are set by the filter data.

The client MAY have to obtain an authorization token before being able to subscribe to the vehicle signal(s). The server MUST issue a notification if a trigger rule is fulfilled. If the server is able to satisfy the request it MUST return a success response. If the server is unable to fulfil the request, then the server MUST return an error response. If an error occurs during the subscription period, the server SHOULD return an error notification.

Arguments, of which path and filter are mandatory:

• path The path as defined in VSS to one or more nodes in the VSS tree.
• filter The rule set describing triggering criterias for issuance of asynchronous notification messages.
• authorization The authorization token.

Success response:

• subscriptionId A handle identifying notification messages associated with the subscription.
• timestamp The start time for the subscription period.

Unsubscribe

Purpose: Termination of the subscription period started by a previous subscribe request.

If the server is able to satisfy the request it MUST return a success response, and it MUST stop issuing notifications associated to the subscription handle. If the server is unable to fulfil the request, then the server MUST return an error response.

Arguments, of which subscriptionId is mandatory:

• subscriptionId Handle identifying the subscription.

Success response:

• subscriptionId Handle identifying the subscription.
• timestamp The stop time for the subscription period.

Subscription

Purpose: Asynchronous client notification according to the subscribe request trigger rules.

The server MUST issue a notification message when a triggering rule associated with the subscription is met. If the server cannot fulfill the triggering rules it MUST issue an error notification and terminate the subscription.

Arguments:

• subscriptionId Handle identifying the subscription.
• data The data structure contains one or more sets of a path and a data point structure.
• path The path for the associated data point structure.
• data point A structure containing one or more tuplets of value and timestamp.
• value The value associated with the filter expression.
• timestamp The capture time of the value.
• timestamp The time of the server subscription execution.

Error Format

The error information has three components - a number, a reason, and a message. The number MUST always be part of the error information, while the reason and message components MAY be a part of it.

• number See VISSv2:TRANSPORT, "Status code" chapter.
• reason See VISSv2:TRANSPORT, "Status code" chapter.
• message See VISSv2:TRANSPORT, "Status code" chapter.

Error Handling

A request addressing multiple nodes may address both valid nodes, and invalid nodes. The latter case shall lead to a Forbidden error (403) response message part that contains information about which node, or nodes, that are invalid. The error response shall not contain data from any of the validly addressed nodes.

Response syntax

A response may contain multiple values, due to either that multiple nodes are addressed, or to that multiple values for one signal is returned. These two reasons can be combined, leading to four different cases.

• Request for a single value from a single node.
• Request for multiple values from a single node.
• Request for a single value from multiple nodes.
• Request for multiple values from multiple nodes.

Response for a single value from a single node:

         
  "data": {
    "dp": {
      "ts": "Z",
      "value": "Y"
    },
    "path": "X"
  }
                   

Response for multiple values from a single node:

  "data": {
    "dp": [
      {
        "ts": "Z1",
        "value": "Y1"
      },
      {
        "ts": "Zn",
        "value": "Yn"
      }
    ],
    "path": "X"
  }
                

Response for a single value from multiple nodes:

        
  "data": [
    {
      "dp": {
        "ts": "Z1",
        "value": "Y1"
      },
      "path": "X1"
    },
    {
      "dp": {
        "ts": "Zm",
        "value": "Ym"
      },
      "path": "Xm"
    }
  ]
                

Response for multiple values from multiple nodes:

         
  "data": [
    {
      "dp": [
        {
          "ts": "Z11",
          "value": "Y11"
        },
        {
          "ts": "Z1n",
          "value": "Y1n"
        }
      ],
      "path": "X1"
    },
    {
      "dp": [
        {
          "ts": "Zm1",
          "value": "Ym1"
        },
        {
          "ts": "Zmn",
          "value": "Ymn"
        }
      ],
      "path": "Xm"
    }
  ]
        

Subscription Notification Triggering

A subscription request must always contain a filter operation that describes the trigger event that leads to that the server dispatches an asynchronous notification message. For the filter types "range" or "change", the triggering is dependent on the signal value. When the request addresses multiple signals, the triggering condition shall only be evaluated on one of the signals, which is the first signal in the value array of paths. The first path in the array must therefore not contain wildcards to address multiple signals. In this case one of the path addresses in the wildcard expression must be selected as the first array element, which can then be followed by the wildcard expression. The duplicate reference to one signal that this leads to shall be resolved by the server to a singleton in the notifications.

Long Term Flow

This section is non-normative.
This flow requires that a client is able to run public key cryptographic primitives, i.e. key pair generation and signatures, and has access to some kind of trusted execution environment where private keys are protected from the regular execution environment. The advantage of using the long term flow is that the client can be trusted with longer expiry times of access grant tokens. A client selects the long term flow by including a public key in the access grant request.

Short Term Flow

This section is non-normative.
This flow does not require the Client to have access to the capabilities needed for the long term flow. In the short term flow the client must due to a shorter expiry time contact the access grant server more often to obtain a new access grant token.
A client selects the short term flow by excluding a public key in the access grant request.

Open Flow

This section is non-normative.
The open flow differs from the long and short term flows in that it does not specify the steps that a client needs to perform to obtain an access token.
The access token used in this flow also differs from the other flows, the Scope and Client context claims are removed, and replaced by a Signal access claim, as shown in .
This means that the only chapters of the Access Control model that relates to the Open flow, besides this chapter, are and .

Access Grant Request

The request shall contain the Context and Proof parameters below, the other two are optional:

• VIN: The vehicle identification number. This may be a pseudo-VIN, or any other identity that uniquely links to the vehicle in the access control ecosystem.
• Context: The context associated to the client. The context consists of a triplet of roles for user, app permissions, and device characteristics.
• Proof: A proof mechanism that is used by the client to attest its context to the access grant server. This is indeed a composed proof for the User role, app permissions, and device characteristics.
• Public key: If this parameter is present, the client will receive a long term access grant token in return.

Depending on the kind of proofs included in the request, the client and the server may need to run an interactive protocol to verify them. The protocol may involve also third parties, such as the ecosystem manager or the resource owner. The protocol is out of scope for this specification.
In scenarios where both the client and the access grant server are deployed in-vehicle the VIN parameter may be omitted, in all other deployment scenarios it shall be present.

Access Grant Response

The response shall contain the parameter below:

• Access grant token: A signed token with claims needed for the validation of the client request.

An error response shall contain the parameter:

• Error code: The error code shall be informative in order for the client to understand what it needs to correct to become successful.

Access Token Request

The request shall contain at least these two parameters below:

• Access grant token: A signed token with claims needed for the validation of the client request.
• Purpose: The intended client usage of the requested data.

The access token server acts as a Policy Enforcement Point, making decisions on whether to grant access to the protected resource based on the provided access grant token and purpose.

Access Token Response

A successful response shall contain the parameter:

• Access token: The token to be used in client requests to the VISSv2 server for Protected Resources.

• Error code: The error code shall be informative in order for the client to understand what it needs to correct to become successful.

Protected Resource Request

This is a VISSv2 request including an access token as described in general in the chapter, and for different transport protocols in the VISSv2 TRANSPORT document.

Protected Resource Response

This is a VISSv2 response as described in general in the chapter, and for different transport protocols in the VISSv2 TRANSPORT document. It does not differ from the response to an unprotected resource request.

Client

This section is non-normative.
The client is an abstract representation of three sub-actors:

• The device. It is in charge of running the Apps that make requests to the VISSv2 server
• The app. It runs requests on behalf of the user.
• The user. It delegates access rights to the app.

Access Grant Server

This section is non-normative.
The access grant server is in charge of producing access grant tokens to clients.
Depending on the capabilities of the client, the specification supports two types of access grant tokens: Short term and long term access grant tokens.
Long term access grant tokens, are supported for those clients able to run public key cryptographic primitives, i.e. key pair generation and signatures, and is the recommended choice for clients with access to a trusted execution environment where private keys are protected from the regular execution environment. The specification also supports short term access grant tokens that require no extra capabilities in the client, but due to its shorter expiry time it forces the client to contact the access grant server more often before access token server requests for an access token.
The client request shall contain the following:

• A client context.
• A set of proofs.

• A VIN.

• A public key.

• To verify the client context, and assess that their respective role request can be granted.
• To check that the vehicle represented by the VIN belong to this Ecosystem, and is accessible.
• To create an access grant token.

Access Token Server

This section is non-normative.
The client shall after a successful interaction with the access grant server request an access token from the access token server. The client request shall contain at least these two parameters below.

• Access grant token.
• Purpose.

• To validate the access grant token.
• To validate that the client context provides permission for the requested purpose.
• To create an access token.

• Signature validation.
• Expiry time check.

Access Control Server

The VISSv2 server MUST support validation of access tokens. The functionality needed for this is decribed in this chapter. This includes validation of at least the following:

• Token signature.
• Token expiry time.
• Token signal scope.
• Token access permission.

The access token need to be refreshed periodically, which is controlled by the expiry time. If the access grant token that the client used to obtain the now expired access token is not expired, then the client can revisit the access token server with this access grant token to obtain a new access token.
If the access grant token is expired, then the client must obtain a new access grant token first, before revisiting the access token server.
The server SHOULD support caching of a limited number of access tokens. The access token MUST be included in the cache after a first successful request and MUST be removed once they expire. The client can decide to include only the jti claim in following requests in order to save bandwith. At any point the server might decide to remove any token from the cache. In this case the client will get a "401, missing_token" error and will be forced to send the whole access token again. For client requests that are not granted due to access control, the VISSv2 server MUST return one of the error codes shown in the table below.

Resource Owner

This section is non-normative.
The resource owner is typically the owner and/or driver of the vehicle. If Consent is required for granting access to the protected resource, then it should be directed to the resource owner. The process for this is out of scope for this specification.

Ecosystem Manager

This section is non-normative.
The Ecosystem manager is the entity responsible for the functionality of the access control system. This typically includes the management of the access grant server, and the access token server, the Policy documents, and that there is a PKI domain for the other actors to utilize.

Client Authentication

This section is non-normative.
The three client sub-actors must provide authentication credentials to the access grant server. This may be certificates that the sub-actors have obtained from a Certificate Authority that is known by the access grant server. The interactions related to this are out of scope.

Access Grant Token

This section is non-normative.

          
          {
            "alg": "ES256",
            "typ": "JWT"
          },
          {
            "vin": "vehicle-id",
            "iat": 1609452095,
            "exp": 1609459199,
            "clx": "user+app+dev",
            "aud": "w3.org/VISSv2",
            "jti": "5967e92e-40e8-5f39-892d-cc0da890db1d"
          }
          

          
          {
            "alg": "ES256",
            "typ": "JWT"
          },
          {
            "vin": "vehicle-id",
            "iat": 1609452095,
            "exp": 1609459199,
            "clx": "user+app+dev",
            "pub": client_pub_key,
            "aud": "w3.org/VISSv2",
            "jti": "5967e92e-40e8-5f39-892d-cc0da890db1d"
          }
          

Access Token

The access token format differ between the long term/short term flows and the Open Flow. The difference is that the access token for the former flows contains the claims "scp" and "clx", while for the latter flow these are replaced with the "sac" claim.

          
          {
            "alg": "HS256",
            "typ": "JWT"
          },
          {
            "vin": "vehicle-id",
            "iat": 1609452095,
            "exp": 1609459199,
            "scp": "PurposeX",
            "clx": "user+app+dev",
            "aud": "w3.org/VISSv2",
            "jti": "5967e93f-40f9-5f39-893e-cc0da890db2e"
          }
          

          
          {
            "alg": "HS256",
            "typ": "JWT"
          },
          {
            "vin": "vehicle-id",
            "iat": 1609452095,
            "exp": 1609459199,
            "sac": signal-set,
            "aud": "w3.org/VISSv2",
            "jti": "5967e93f-40f9-5f39-893e-cc0da890db2e"
          }
          

Proof of Possession

Long term access grant tokens need to be accompanied by a Proof of Possession (PoP) for the private key corresponding to the public key included in the access grant token. This requirement enables a longer validity for this kind of tokens, ranging from a few days to a even a year. By adding the PoP, we prevent an eavesdropper to reuse an access token request, impersonating the client. Without a PoP, the longer the validity of an access grant token, the higher the risk an attacker could intercept and reuse it. PoP for JWT are defined in [[RFC7800]], but in essence, a PoP enables the requester to proof to the server that it has access to a private key, without disclosing it. Traditionally that would require the server to create a random challenge, or nonce, and ask the client to sign it with its private key. Along with the public key, the server would be able to verify the PoP. This scheme would require an extra step in the protocols, where the client ask for the nonce.

In order to avoid this extra step, the client can generate the nonce itself. The server would need to check that nonces are not reused. Although logging previous nonces at the server side would work for small environments, we propose the use of an incremental nonce in the form of a timestamp. One of the drawbacks of this proposal is that the server has no means to check whether the PoP has been precomputed or not. However, this is irrelevant from the eavesdropper point of view.

In case freshness of the PoP was a critical requirement, we could use a public source of randomness to obtain the nonce, e.g. Leage of Entropy or Interoperable Randomness Beacons. That would provide the server a mean to check freshness of the PoP but on the other hand, it would require the client to access the public source of randomness every time it needs to create a PoP which is against the main design goals for the long term access grant token.

User Roles

VISSv2 specifies the following minimum set of roles for users:

• OEM
• Dealer
• Independent
• Owner
• Driver
• Passenger

Application Roles

VISSv2 specifies the following minimum set of roles for applications:

• OEM
• Third party

Device Roles

VISSv2 specifies the following minimum set of roles for devices:

• Vehicle
• Nomadic
• Cloud

Purpose List

A client shall provide a purpose as input to a request for an access token. A list of supported purposes needs to exist for a client to select from. The ecosystem manager shall therefore provide means for clients to survey the list to find a purpose that fits its use case.
Each entry in the list contains a short description of the purpose, which is what the client shall provide as input to its request for an access token. There is also a long purpose description, which may be used in the dialogue for consent, if needed. Then there is a list of the client context, i. e. the sub-actor role triplet, that can be granted this access. Finally the signals that the client is given access to for this purpose are defined. Each signal is defined by an object containing the signal path and its access permission, the latter being either "read-only", or "read-write". For multiple signals a JSON array is used, as shown in the example below.

        {"purposes":
            [{"short": "fuel-status", 
            "long": "Fuel level and remaining range.", 
            "contexts":[{"user":"Independent","app":["OEM", "Third party"], "device":"Cloud"}, {"user":"Owner", "app":"Third party", "device":"Nomadic"}, {"user":"Driver", "app":"OEM", "device":"Vehicle"}], 
            "signal_access":
                [{"path": "Vehicle.Powertrain.FuelSystem.Level", "access_permission": "read-only"}, 
                {"path": "Vehicle.Powertrain.FuelSystem.Range", "access_permission": "read-only"}] 
            }, 
            {}] 
        }
        

Scope List

The scope list contains a list of the VSS tree nodes for which access shall be prohibited, per client context. This prohibition is regardless of whether the client has a valid access token or not.
The scope list can also be used to limit the node metadata that is returned on a service discovery request.
Each entry in the list contains a list of paths to nodes that should be excluded, and a list of the client contexts, i. e. the sub-actor role triplet, for which this exclusion should be made.
The scope list may contain an entry for a context with all three Roles set to "Undefined". The no-access scope of this entry shall then be used for signal discovery requests where no token is included.
The list shall use a JSON format as shown in the example below.

        {"scope":
            [{"contexts":[ { "user":["Driver", "Passenger"], "app":"Third party", "device":"Vehicle"}, { } ], 
            "no_access":
                ["Vehicle.Drivetrain.Transmission.Speed", 
                "Vehicle.CurrentLocation.Latitude", 
                "Vehicle.CurrentLocation.Longitude"]
            }, 
            {}] 
        }