[Openid-specs-mobile-profile] How to authenticate mobile apps with private-key-jwt without issuing ClientIDs or managing public keys

[sm-tanaka at kddi.com]

Dear Members of AB/Connect Working Group and MODRNA Working Group,


I hope this message finds you well.

We are considering implementing client authentication using private-key-jwt on mobile apps.
In this context, we have identified the following challenges:

Since the key pairs generated within devices differ for each device,
we need an identifier on the server side to determine which device's public key is being used.
One potential solution is to issue a Client ID for each device during "OpenID Connect Dynamic Client Registration 1.0" process.
However, this raises the issue of managing a vast number of client IDs on the server side.
To address this issue, I would appreciate your insights on the following two questions:

Though the vast number of Client IDs appears to be a challenge unique to mobile use cases,
I believe similar challenges may exist in the context of wallet use cases.
Are there any proposed solutions or discussions about this issue in the standard specifications?

We are considering having the server issue the public key certificate for the application's public key.
Thereafter, the application would present both the client assertion and the public key certificate,
allowing the server to validate the client assertion without storing the public key.
We would like to implement this in accordance with standard specifications.
Is there a standard method to embed the public key certificate within the JWT of the client assertion?
I found that RFC 7515, section 4.1.6 proposes a method for embedding public key certificate in the JWT header.
Is RFC 7515 applicable to our use case?, and are there any real use cases that utilize RFC 7515?

Thank you for your time and assistance. I look forward to your insights on these matters.

Best regards,
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田中　翔真　(Shoma Tanaka)
ＫＤＤＩ株式会社
パーソナル事業本部
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E-mail：sm-tanaka at kddi.com
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