Draft: draft-ietf-ace-oscore-profile

Commentary: Including comments from  's review :
Mailing list commentary: Hello OSCORE profile authors and ACE , Please , find below some WGLC comments . Hope it helps ! Best , /Marco Section 1 s / is not done by a / is not achieved through a s / after the first OSCORE exchange / after the first message exchange using OSCORE Section 2 " This specific identifier , encoded as a byte string , is assigned by the AS to be unique in the sets of its OSCORE Security Contexts ... " To avoid confusion , it 's probably better to say " unique among the issued sets of OSCORE input material " , since the AS can have actual OSCORE Security Contexts it uses to communicate with Clients or Resource Servers . Referring to ' i d ' as specific identifier , the text says : " and is not used as input material to derive the full OSCORE Security Context . " That 's correct , but then the identifier is later included in Table 1 " OSCOREInputMaterial Parameters " :-) Perhaps it 's fine to just revert to OSCORESecurityContextObject , both for the name of Table 1 and in different spots of the text ? They would still consider ' i d ' as OSCORE Input Material Identifier , while aligned with the registry name from Section 9.4 . s / If the request verifies / If the request is successfully verified s / until token expiration / until token deletion , due to e.g. expiration or revocation s / the same or different / the same or a different one Figure 1 can also show the achievement of mutual authentication , following the OSCORE exchange at the end Section 3.1 s / object . kid field carrying / object , with the kid field carrying Section 3.2 " ... profile negotiation can be omitted " - I think " profile signaling " better reflects what may happen here , see also the beginning of the paragraph . s / in the the / in the s / in the ' cnf ' parameter of the token / in the ' cnf ' claim of the token Section 3.2.1 In the text entries following Table 1 , the CBOR integer labels need to be aligned with the CDDL summary at the end of the section . s / This parameter identifies the OSCOREInputMaterial / This parameter identifies the OSCOREInputMaterial object s / the " i d " type is byte string / the " i d " type is bstr This version -13 has removed ' clientId ' and ' serverId ' from Table 1 and thus as code points from the " OSCORE Security Context Parameters " registry . No strong need to include them back , but even if this profile does not use them and does not send them on the wire , I think they still belong to the same namespace , since they are descriptive of a security context and are in fact also used as input material to derive it :-) Section 4 s / the RS and client authenticates themselves / the RS and client authenticate each other s / successfully verified the response from the RS / successfully verified a response from the RS as protected with the established OSCORE context ( similar occurrences are also later in the text ) Section 4.1 In the first paragraph , I suggest to rephrase as " and the posted access token is still retained " . That does n't require to explicitly mention " valid " , since asserting especially validity can be non - trivial for the client , e.g. in case of Token revocation . ( similar occurrences are also later in the text ) In the second paragraph , I suggest to extend the ending as : " ... makes sure that it does not collide with any of its Recipient IDs currently used . These include also Recipient IDs used as ID1 value for ongoing executions of this profile . " s / the client the token and N1 in a CBOR map / the client the token , N1 and ID1 in a CBOR map s / using the " accesstoken " parameter / using the ' accesstoken ' parameter In the sixth paragraph , the last sentence says " ... as different nonces will be used . " Does n't the client and the RS also negotiate new IDs like they did in the first posting of the same original token ? In the last paragraph : " The client MUST only send the access token in the payload , no nonce or identifier are sent . " Just to be sure , can you expand on this request format ? I suppose the client still uses Content - Format " application / ace+cbor " , just including only the ' accesstoken ' entry in the map . Correct ? In the last paragraph : " ... the RS will replace the old token with the new one , maintaining the same Security Context . " This replacement step can be expanded for clarity . A simple 1 - to-1 replacement would overwrite also the stored ' cnf ' claim from the original token , among other things . So it should be more about selectively replacing some information originally coming the first token , while keeping some other from it . What to actually replace should include , for instance , information related to access rights ( e.g. scope ) , and to the new token 's lifetime ( exp , exi ) . While reading this , I was wondering if one could repost the same first token to rekey the OSCORE context . This is mentioned at the end of Section 4.3 , but anticipating the possibility here and adding a forward pointer to Section 4.3 would help . Section 4.1.1 and Section 4.1.2 The first sentence captures the case where the first token is posted or re - posted . It can be rephrased to cover also the posting of a token for updating access rights , where these parameters are not included . Section 4.2 " any of the mandatory parameters from the AS or the identifier ) ... " It 's worth making it explicit that the mentioned identifier is ' i d ' . s / in the ' osc'/in the ' osc ' field " ... the RS must respond " --- Should this not be a MUST ? s / is different from the aceclientrecipientid / is different from the value specified in the received ' aceclientrecipientid ' parameter Second paragraph after Figure 11 s / MUST discard / MUST ignore s / the " cnf " parameter of / the ' cnf ' claim ofs / matches the OSCORE Input / matches with the identifier of the OSCORE Input Related to a previous comment about token replacement , some information has to be retained from the first token , as not present in the new one .
Paragraph (version A):
proof of possession is not done by a dedicated protocol element, but
rather occurs after the first OSCORE exchange.
Paragraph (version B):
proof of possession is not achieved through a dedicated protocol
element, but rather occurs after the first message exchange using
OSCORE.
Paragraph (version A):
Finally, the client sends a request protected with OSCORE to the RS.
If the request verifies, the server stores the complete Security
Context state that is ready for use in protecting messages, and uses
it in the response, and in further communications with the client,
until token expiration.  This Security Context is discarded when a
token (whether the same or different) is used to successfully derive
a new Security Context for that client.
Paragraph (version B):
Finally, the client sends a request protected with OSCORE to the RS.
If the request is successfully verified, the server stores the
complete Security Context state that is ready for use in protecting
messages, and uses it in the response, and in further communications
with the client, until token deletion, due to e.g. expiration.  This
Security Context is discarded when a token (whether the same or a
different one) is used to successfully derive a new Security Context
for that client.
Paragraph (version A):
After the whole message exchange has taken place, the client can
contact the AS to request an update of its access rights, sending a
similar request to the token endpoint that also includes an
identifier so that the AS can find the correct OSCORE security
material it has previously shared with the client.  This specific
identifier, encoded as a byte string, is assigned by the AS to be
unique in the sets of its OSCORE Security Contexts, and is not used
as input material to derive the full OSCORE Security Context.
Paragraph (version B):
After the whole message exchange has taken place, the client can
contact the AS to request an update of its access rights, sending a
similar request to the token endpoint that also includes an
identifier so that the AS can find the correct OSCORE security input
material it has previously shared with the client.  This specific
identifier, encoded as a byte string, is assigned by the AS to be
unique in the sets of its OSCORE security input materials, and is not
used as input material to derive the full OSCORE Security Context.
Paragraph (version A):
If the client wants to update its access rights without changing an
existing OSCORE Security Context, it MUST include in its POST request
to the token endpoint a req_cnf object. kid field carrying a CBOR
byte string containing the OSCORE_Input_Material Identifier (assigned
as discussed in as-c).  This identifier, together with other
information such as audience (see Section 5.6.1 of I-D.ietf-ace-
oauth-authz), can be used by the AS to determine the shared secret
bound to the proof-of-possession token and therefore MUST identify a
symmetric key that was previously generated by the AS as a shared
secret for the communication between the client and the RS.  The AS
MUST verify that the received value identifies a proof-of-possession
key that has previously been issued to the requesting client.  If
that is not the case, the Client-to-AS request MUST be declined with
the error code 'invalid_request' as defined in Section 5.6.3 of I-
D.ietf-ace-oauth-authz.
Paragraph (version B):
If the client wants to update its access rights without changing an
existing OSCORE Security Context, it MUST include in its POST request
to the token endpoint a req_cnf object, with the kid field carrying a
CBOR byte string containing the OSCORE_Input_Material Identifier
(assigned as discussed in as-c).  This identifier, together with
other information such as audience (see Section 5.6.1 of I-D.ietf-
ace-oauth-authz), can be used by the AS to determine the shared
secret bound to the proof-of-possession token and therefore MUST
identify a symmetric key that was previously generated by the AS as a
shared secret for the communication between the client and the RS.
The AS MUST verify that the received value identifies a proof-of-
possession key that has previously been issued to the requesting
client.  If that is not the case, the Client-to-AS request MUST be
declined with the error code 'invalid_request' as defined in
Section 5.6.3 of I-D.ietf-ace-oauth-authz.
Paragraph (version A):
The AS can signal that the use of OSCORE is REQUIRED for a specific
access token by including the "profile" parameter with the value
"coap_oscore" in the access token response.  This means that the
client MUST use OSCORE towards all resource servers for which this
access token is valid, and follow oscore-setup to derive the security
context to run OSCORE.  Usually it is assumed that constrained
devices will be pre-configured with the necessary profile, so that
this kind of profile negotiation can be omitted.
Paragraph (version B):
The AS can signal that the use of OSCORE is REQUIRED for a specific
access token by including the "profile" parameter with the value
"coap_oscore" in the access token response.  This means that the
client MUST use OSCORE towards all resource servers for which this
access token is valid, and follow oscore-setup to derive the security
context to run OSCORE.  Usually it is assumed that constrained
devices will be pre-configured with the necessary profile, so that
this kind of profile signaling can be omitted.
Paragraph (version A):
This data is transported in the the OSCORE_Input_Material.  The
OSCORE_Input_Material is a CBOR map object, defined in oscore-sec-
ctx.  This object is transported in the 'cnf' parameter of the access
token response as defined in Section 3.2 of I-D.ietf-ace-oauth-
params, as the value of a field named 'osc', registered in osc-cwt
and osc-jwt.
Paragraph (version B):
This data is transported in the OSCORE_Input_Material.  The
OSCORE_Input_Material is a CBOR map object, defined in oscore-sec-
ctx.  This object is transported in the 'cnf' parameter of the access
token response as defined in Section 3.2 of I-D.ietf-ace-oauth-
params, as the value of a field named 'osc', registered in osc-cwt
and osc-jwt.
Paragraph (version A):
The master secret and the identifier of the OSCORE_Input_Material
MUST be communicated as the 'ms' and 'id' field in the 'osc' field in
the 'cnf' parameter of the access token response.  If included, the
AEAD algorithm is sent in the 'alg' parameter in the
OSCORE_Input_Material; the HKDF algorithm in the 'hkdf' parameter of
the OSCORE_Input_Material; a salt in the 'salt' parameter of the
OSCORE_Input_Material; and the OSCORE version in the 'version'
parameter of the OSCORE_Input_Material.
Paragraph (version B):
The master secret and the identifier of the OSCORE_Input_Material
MUST be communicated as the 'ms' and 'id' field in the 'osc' field in
the 'cnf' parameeter of the access token response.  If included, the
AEAD algorithm is sent in the 'alg' parameter in the
OSCORE_Input_Material; the HKDF algorithm in the 'hkdf' parameter of
the OSCORE_Input_Material; a salt in the 'salt' parameter of the
OSCORE_Input_Material; and the OSCORE version in the 'version'
parameter of the OSCORE_Input_Material.
Paragraph (version A):
If the client has requested an update to its access rights using the
same OSCORE Security Context, which is valid and authorized, the AS
MUST omit the 'cnf' parameter in the response, and MUST carry the
OSCORE Input Material identifier in the 'kid' field in the 'cnf'
parameter of the token.  This identifier needs to be included in the
token in order for the RS to identify the correct OSCORE Input
Material.
Paragraph (version B):
If the client has requested an update to its access rights using the
same OSCORE Security Context, which is valid and authorized, the AS
MUST omit the 'cnf' parameter in the response, and MUST carry the
OSCORE Input Material identifier in the 'kid' field in the 'cnf'
claim of the token.  This identifier needs to be included in the
token in order for the RS to identify the correct OSCORE Input
Material.
Paragraph (version A):
This parameter identifies the OSCORE Version number, which is an
unsigned integer.  For more information about this field, see
section 5.4 of RFC8613.  In JSON, the "version" value is an
integer.  In CBOR, the "version" type is int, and has label 0.
Paragraph (version A):
This parameter identifies the OSCORE Master Secret value, which is
a byte string.  For more information about this field, see section
string.  In CBOR, the "ms" type is bstr, and has label 1.
Paragraph (version B):
This parameter identifies the OSCORE Version number, which is an
unsigned integer.  For more information about this field, see
section 5.4 of RFC8613.  In JSON, the "version" value is an
integer.  In CBOR, the "version" type is integer, and has label 0.
Paragraph (version B):
This parameter identifies the OSCORE Master Secret value, which is
a byte string.  For more information about this field, see section
string.  In CBOR, the "ms" type is byte string, and has label 1.
Paragraph (version A):
This parameter identifies the OSCORE HKDF Algorithm.  For more
information about this field, see section 3.1 of RFC8613.  The
values used MUST be registered in the IANA "COSE Algorithms"
registry (see COSE.Algorithms) and MUST be HMAC-based HKDF
algorithms.  The value can either be the integer or the text
string value of the HMAC-based HKDF algorithm in the "COSE
Algorithms" registry.  In JSON, the "hkdf" value is a case-
sensitive ASCII string or an integer.  In CBOR, the "hkdf" type is
tstr or int, and has label 4.
Paragraph (version B):
This parameter identifies the OSCORE HKDF Algorithm.  For more
information about this field, see section 3.1 of RFC8613.  The
values used MUST be registered in the IANA "COSE Algorithms"
registry (see COSE.Algorithms) and MUST be HMAC-based HKDF
algorithms.  The value can either be the integer or the text
string value of the HMAC-based HKDF algorithm in the "COSE
Algorithms" registry.  In JSON, the "hkdf" value is a case-
sensitive ASCII string or an integer.  In CBOR, the "hkdf" type is
text string or integer, and has label 4.
Paragraph (version A):
This parameter identifies the OSCORE AEAD Algorithm.  For more
information about this field, see section 3.1 of RFC8613 The
values used MUST be registered in the IANA "COSE Algorithms"
registry (see COSE.Algorithms) and MUST be AEAD algorithms.  The
value can either be the integer or the text string value of the
HMAC-based HKDF algorithm in the "COSE Algorithms" registry.  In
JSON, the "alg" value is a case-sensitive ASCII string or an
integer.  In CBOR, the "alg" type is tstr or int, and has label 5.
Paragraph (version A):
This parameter identifies an input to the OSCORE Master Salt
value, which is a byte string.  For more information about this
field, see section 3.1 of RFC8613.  In JSON, the "salt" value is a
Base64 encoded byte string.  In CBOR, the "salt" type is bstr, and
has label 6.
Paragraph (version A):
This parameter identifies the security context as a byte string.
This identifier is used as OSCORE ID Context.  For more
information about this field, see section 3.1 of RFC8613.  In
JSON, the "contextID" value is a Base64 encoded byte string.  In
CBOR, the "contextID" type is bstr, and has label 7.
Paragraph (version B):
This parameter identifies the OSCORE AEAD Algorithm.  For more
information about this field, see section 3.1 of RFC8613 The
values used MUST be registered in the IANA "COSE Algorithms"
registry (see COSE.Algorithms) and MUST be AEAD algorithms.  The
value can either be the integer or the text string value of the
HMAC-based HKDF algorithm in the "COSE Algorithms" registry.  In
JSON, the "alg" value is a case-sensitive ASCII string or an
integer.  In CBOR, the "alg" type is text string or integer, and
has label 5.
Paragraph (version B):
This parameter identifies an input to the OSCORE Master Salt
value, which is a byte string.  For more information about this
field, see section 3.1 of RFC8613.  In JSON, the "salt" value is a
Base64 encoded byte string.  In CBOR, the "salt" type is byte
string, and has label 6.
Paragraph (version B):
This parameter identifies the security context as a byte string.
This identifier is used as OSCORE ID Context.  For more
information about this field, see section 3.1 of RFC8613.  In
JSON, the "contextID" value is a Base64 encoded byte string.  In
CBOR, the "contextID" type is byte string, and has label 7.
Paragraph (version A):
Note that the RS and client authenticates themselves by generating
the shared OSCORE Security Context using the pop-key as master
secret.  An attacker posting a valid token to the RS will not be able
to generate a valid OSCORE context and thus not be able to prove
possession of the pop-key.  Additionally, the mutual authentication
is only achieved after the client has successfully verified the
response from the RS.
Paragraph (version B):
Note that the RS and client authenticates each other by generating
the shared OSCORE Security Context using the pop-key as master
secret.  An attacker posting a valid token to the RS will not be able
to generate a valid OSCORE Security Context and thus not be able to
prove possession of the pop-key.  Additionally, the mutual
authentication is only achieved after the client has successfully
verified a response from the RS protectd with the generated OSCORE
Security Context.
Paragraph (version A):
The client MUST generate a nonce value very unlikely to have been
previously used with the same input keying material.  This profile
RECOMMENDS to use a 64-bit long random number as nonce's value.  The
client MUST store the nonce N1 as long as the response from the RS is
not received and the access token related to it is still valid.
Paragraph (version A):
The client generates its own Recipient ID, ID1, for the OSCORE
Security Context that it is establishing with the RS.  By generating
its own Recipient ID, the client makes sure that it does not collide
with any of its Recipient IDs.
Paragraph (version B):
The client MUST generate a nonce value very unlikely to have been
previously used with the same input keying material.  This profile
RECOMMENDS to use a 64-bit long random number as nonce's value.  The
client MUST store the nonce N1 as long as the response from the RS is
not received and the access token related to it is still valid (to
the best of the client's knowledge).
Paragraph (version B):
The client generates its own Recipient ID, ID1, for the OSCORE
Security Context that it is establishing with the RS.  By generating
its own Recipient ID, the client makes sure that it does not collide
with any of its Recipient IDs, nor with any other identifier ID1 if
the client is executing this exchange with a different RS at the same
time.
Paragraph (version A):
Note that the use of the payload and the Content-Format is different
from what is described in section 5.8.1 of I-D.ietf-ace-oauth-authz,
which only transports the token without any CBOR wrapping.  In this
profile, the client MUST wrap the token and N1 in a CBOR map.  The
client MUST use the Content-Format "application/ace+cbor" defined in
section 8.14 of I-D.ietf-ace-oauth-authz.  The client MUST include
the access token using the "access_token" parameter, N1 using the
'nonce1' parameter defined in nonce1, and ID1 using the
'ace_client_recipientid' parameter defined in id1.
Paragraph (version B):
Note that the use of the payload and the Content-Format is different
from what is described in section 5.8.1 of I-D.ietf-ace-oauth-authz,
which only transports the token without any CBOR wrapping.  In this
profile, the client MUST wrap the token, N1 and ID1 in a CBOR map.
The client MUST use the Content-Format "application/ace+cbor" defined
in section 8.14 of I-D.ietf-ace-oauth-authz.  The client MUST include
the access token using the 'access_token' parameter, N1 using the
'nonce1' parameter defined in nonce1, and ID1 using the
'ace_client_recipientid' parameter defined in id1.
Paragraph (version B):
The client may also chose to re-POST the access token in order to
renew its OSCORE Security Context.  In that case, the client and the
RS will exchange newly generated nonces, re-negotiate identifiers,
and derive new keying material.  The client and RS might decide to
keep the same identifiers or renew them during the re-negotiation.
Paragraph (version A):
If the client has already posted a valid token, has already
established a security association with the RS, and wants to update
its access rights, the client can do so by posting the new token
(retrieved from the AS and containing the update of access rights) to
the /authz-info endpoint.  The client MUST protect the request using
the OSCORE Security Context established during the first token
exchange.  The client MUST only send the access token in the payload,
no nonce or identifier are sent.  After proper verification (see rs-
c), the RS will replace the old token with the new one, maintaining
the same Security Context.
Paragraph (version B):
If the client has already posted a valid token, has already
established a security association with the RS, and wants to update
its access rights, the client can do so by posting the new token
(retrieved from the AS and containing the update of access rights) to
the /authz-info endpoint.  The client MUST protect the request using
the OSCORE Security Context established during the first token
exchange.  The client MUST only send the 'access_token' field in the
CBOR map in the payload, no nonce or identifier are sent.  After
proper verification (see rs-c), the RS will replace the old token
with the new one, maintaining the same Security Context.
Paragraph (version A):
The RS MUST follow the procedures defined in section 5.8.1 of I-
D.ietf-ace-oauth-authz: the RS must verify the validity of the token.
If the token is valid, the RS must respond to the POST request with
that the RS cannot process (e.g., an unknown scope), or if any of the
expected parameters is missing (e.g., any of the mandatory parameters
from the AS or the identifier), or if any parameters received in the
'osc' is unrecognized, the RS must respond with an error response
code equivalent to the CoAP code 4.00 (Bad Request).  In the latter
two cases, the RS may provide additional information in the error
response, in order to clarify what went wrong.  The RS may make an
introspection request (see Section 5.7.1 of I-D.ietf-ace-oauth-authz)
to validate the token before responding to the POST request to the
authz-info endpoint.
Paragraph (version A):
Additionally, the RS MUST generate a nonce N2 very unlikely to have
been previously used with the same input keying material, and its own
Recipient ID, ID2.  The RS makes sure that ID2 does not collide with
any of its Recipient IDs.  The RS MUST ensure that ID2 is different
from the ace_client_recipientid.  The RS sends N2 and ID2 within the
MUST be a CBOR map containing the 'nonce2' parameter defined in
nonce2, set to N2, and the 'ace_server_recipientid' parameter defined
in id2, set to ID2.  This profile RECOMMENDS to use a 64-bit long
random number as nonce's value.  The RS MUST use the Content-Format
"application/ace+cbor" defined in section 8.14 of I-D.ietf-ace-oauth-
authz.
Paragraph (version B):
The RS MUST follow the procedures defined in section 5.8.1 of I-
D.ietf-ace-oauth-authz: the RS must verify the validity of the token.
If the token is valid, the RS must respond to the POST request with
that the RS cannot process (e.g., an unknown scope), or if any of the
expected parameters is missing (e.g., any of the mandatory parameters
from the AS or the identifier 'id1'), or if any parameters received
in the 'osc' field is unrecognized, the RS must respond with an error
response code equivalent to the CoAP code 4.00 (Bad Request).  In the
latter two cases, the RS may provide additional information in the
error response, in order to clarify what went wrong.  The RS may make
an introspection request (see Section 5.7.1 of I-D.ietf-ace-oauth-
authz) to validate the token before responding to the POST request to
the authz-info endpoint.
Paragraph (version B):
Additionally, the RS MUST generate a nonce N2 very unlikely to have
been previously used with the same input keying material, and its own
Recipient ID, ID2.  The RS makes sure that ID2 does not collide with
any of its Recipient IDs.  The RS MUST ensure that ID2 is different
from the value received in the ace_client_recipientid parameter.  The
RS sends N2 and ID2 within the 2.01 (Created) response.  The payload
of the 2.01 (Created) response MUST be a CBOR map containing the
'nonce2' parameter defined in nonce2, set to N2, and the
'ace_server_recipientid' parameter defined in id2, set to ID2.  This
profile RECOMMENDS to use a 64-bit long random number as nonce's
value.  The RS MUST use the Content-Format "application/ace+cbor"
defined in section 8.14 of I-D.ietf-ace-oauth-authz.
Paragraph (version A):
If the RS receives the token in a OSCORE protected message, it means
that the client is requesting an update of access rights.  The RS
MUST discard any nonce and identifiers in the request, if any was
sent.  The RS MUST check that the "kid" of the "cnf" parameter of the
new access token matches the OSCORE Input Material of the context
used to protect the message.  If that is the case, the RS MUST
discard the old token and associate the new token to the Security
Context identified by the "kid" value in the "cnf" parameter.  The RS
MUST respond with a 2.01 (Created) response protected with the same
Security Context, with no payload.  If any verification fails, the RS
MUST respond with a 4.01 (Unauthorized) error response.
Paragraph (version B):
If the RS receives the token in a OSCORE protected message, it means
that the client is requesting an update of access rights.  The RS
MUST ignore any nonce and identifiers in the request, if any was
sent.  The RS MUST check that the "kid" of the 'cnf' claim of the new
access token matches the identifier of the OSCORE Input Material of
the context used to protect the message.  If that is the case, the RS
MUST overwrite the old token and associate the new token to the
Security Context identified by the "kid" value in the 'cnf' claim.
The RS MUST respond with a 2.01 (Created) response protected with the
same Security Context, with no payload.  If any verification fails,
the RS MUST respond with a 4.01 (Unauthorized) error response.
Paragraph (version A):
The client then uses this Security Context to send requests to RS
using OSCORE.
Paragraph (version B):
The client then uses this Security Context to send requests to the RS
using OSCORE.
Paragraph (version A):
The RS then uses this Security Context to verify requests and send
responses to C using OSCORE.  If OSCORE verification fails, error
responses are used, as specified in section 8 of RFC8613.
Additionally, if OSCORE verification succeeds, the verification of
access rights is performed as described in section tok-ver.  The RS
MUST NOT use the Security Context after the related token has
expired, and MUST respond with a unprotected 4.01 (Unauthorized)
error message to requests received that correspond to a Security
Context with an expired token.
Paragraph (version B):
The RS then uses this Security Context to verify requests and send
responses to the client using OSCORE.  If OSCORE verification fails,
error responses are used, as specified in section 8 of RFC8613.
Additionally, if OSCORE verification succeeds, the verification of
access rights is performed as described in section tok-ver.  The RS
MUST NOT use the Security Context after the related token has
expired, and MUST respond with a unprotected 4.01 (Unauthorized)
error message to requests received that correspond to a Security
Context with an expired token.
Paragraph (version A):
access token as described in c-rs, but without updating the ID
Context.
Paragraph (version B):
access token to the unprotected /authz-info endpoint at the RS, as
described in c-rs, but without updating the ID Context.
Paragraph (version A):
As specified in the ACE framework (section 5.7 of I-D.ietf-ace-oauth-
authz), the requesting entity (RS and/or client) and the AS
communicates via the introspection or token endpoint.  The use of
CoAP and OSCORE (RFC8613) for this communication is RECOMMENDED in
this profile, other protocols (such as HTTP and DTLS or TLS) MAY be
used instead.
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As specified in the ACE framework (section 5.7 of I-D.ietf-ace-oauth-
authz), the requesting entity (RS and/or client) and the AS
communicates via the introspection or token endpoint.  The use of
CoAP and OSCORE (RFC8613) for this communication is RECOMMENDED in
this profile; other protocols (such as HTTP and DTLS or TLS) MAY be
used instead.
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the access token associated with the context expires.
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the access token associated with the context becomes invalid, due
to e.g. expiration.
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OSCORE is designed to secure point-to-point communication, providing
a secure binding between the request and the response(s).  Thus the
basic OSCORE protocol is not intended for use in point-to-multipoint
communication (e.g., multicast, publish-subscribe).  Implementers of
this profile should make sure that their usecase corresponds to the
expected use of OSCORE, to prevent weakening the security assurances
provided by OSCORE.
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OSCORE is designed to secure point-to-point communication, providing
a secure binding between the request and the response(s).  Thus the
basic OSCORE protocol is not intended for use in point-to-multipoint
communication (e.g., multicast, publish-subscribe).  Implementers of
this profile should make sure that their use case corresponds to the
expected use of OSCORE, to prevent weakening the security assurances
provided by OSCORE.
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This profile recommends that the RS maintains a single access token
for a client.  The use of multiple access tokens for a single client
increases the strain on the resource server as it must consider every
access token and calculate the actual permissions of the client.
Also, tokens indicating different or disjoint permissions from each
other may lead the server to enforce wrong permissions.  If one of
the access tokens expires earlier than others, the resulting
permissions may offer insufficient protection.  Developers should
avoid using multiple access tokens for a client.
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If a single OSCORE_Input_Material is used with multiple RSs, the RSs
can impersonate C to one of the other RS, and impersonate another RS
to the client.  If a master secret is used with several clients, the
Cs can impersonate RS to one of the other C.  Similarly if symmetric
keys are used to integrity protect the token between AS and RS and
the token can be used with multiple RSs, the RSs can impersonate AS
to one of the other RS.  If the token key is used for any other
communication between the RSs and AS, the RSs can impersonate each
other to the AS.
Paragraph (version B):
This profile recommends that the RS maintains a single access token
for each client.  The use of multiple access tokens for a single
client increases the strain on the resource server as it must
consider every access token and calculate the actual permissions of
the client.  Also, tokens indicating different or disjoint
permissions from each other may lead the server to enforce wrong
permissions.  If one of the access tokens expires earlier than
others, the resulting permissions may offer insufficient protection.
Developers should avoid using multiple access tokens for a same
client.
Paragraph (version B):
If a single OSCORE_Input_Material is used with multiple RSs, the RSs
can impersonate the client to one of the other RS, and impersonate
another RS to the client.  If a master secret is used with several
clients, the clients can impersonate RS to one of the other clients.
Similarly if symmetric keys are used to integrity protect the token
between AS and RS and the token can be used with multiple RSs, the
RSs can impersonate AS to one of the other RS.  If the token key is
used for any other communication between the RSs and AS, the RSs can
impersonate each other to the AS.