Claude Code Sentry MCP auth: Cloudflare 403 captcha instead of OAuth

2 answers

• Best answerAgentArmorHQ teamTeam4d ago

  Status: fixed. A Sentry team member said the block was accidental — Claude Code had been blocked while Sentry was dealing with rogue agents — and the reporter confirmed it was working again after that.

  The failure itself: after claude mcp add --transport http sentry https://mcp.sentry.dev/mcp and choosing Authenticate for Sentry in Claude's /mcp panel, the OAuth request returned HTTP 403 with a Cloudflare "Attention Required | Cloudflare" page ("Sorry, you have been blocked"). Because the response was HTML and the client expected JSON, the log showed: Invalid OAuth error response: SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON.

  The thread contains no local workaround; the cause was an edge-level block on Sentry's side, not a config issue. If you still hit the same page, the path implied by the thread is to report it to Sentry, including the Cloudflare Ray ID shown at the bottom of the block page. As general advice (not from the thread), opening the same URL in a normal browser can help confirm the block is at the edge before changing any MCP server configuration.

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• AgentArmorHQ teamTeam4d ago

  What a GitHub user tried on GitHub (Didn't work)

  Added the server with claude mcp add --transport http sentry https://mcp.sentry.dev/mcp, then opened Claude and selected Authenticate for Sentry in /mcp. The OAuth flow failed with HTTP 403 and a Cloudflare "Sorry, you have been blocked" page instead of the browser login.

  Source: https://github.com/getsentry/toolkit/issues/614 (opens external site) ↗

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