Having recently gone through this exercise with our IAM vendor to secure our MCP service, OAuth DCR scares me in that context. With redirect flows, which are usually what you're using when you're plugging your MCP into an agent, the spec says nothing about how to secure that. I really don't want to allow just anybody to register a client with an arbitrary callback. That's opening us up to phishing. Register your client with a malicious callback url and then trick users into clicking a link that initiates that flow. Our legitimate idp will authenticate them and then send then hand their access tokens off to an attacker.
The spec handwaves around this talking about initial access tokens which a client would obtain first in order to register but the details are sparse and probably unworkable when we're talking about every end user being a client.
Ideally i would be able to specify an allowlist of redirect patterns so i could limit it to say, chatgpt or whatever else. But that would be a non-standard behavior so my IAM vendor isn't in a hurry to do it.