Fix OAuth redirect_uri_mismatch Errors
An OAuth redirect URI mismatch means the callback in the authorization flow does not satisfy the client's registered policy. Compare the decoded values character by character.
Capture three callback values
Compare the redirect URI registered with the provider, the decoded redirect_uri sent to the authorization endpoint, and the value sent during token exchange when required. Record only the callback and non-secret client metadata. Never log authorization codes, state values, PKCE verifiers, access tokens, refresh tokens, client secrets, or cookies.
Compare every URL component
Check scheme, hostname, port, path, trailing slash, capitalization, and any fixed query component. http://example.com/callback and https://example.com/callback are different. So are /callback and /callback/. Providers vary in normalization rules, so use an explicit callback copied from the registration rather than relying on browser URL equivalence.
Encode the parameter once
Build the authorization URL with a URL API that encodes the redirect URI as one query parameter. Do not pre-encode it and then pass it through another encoder. Inspect the decoded query value, not only the percent-encoded URL. Preserve the identical logical value during the token request instead of rebuilding it from whichever host received the callback.
Fix reverse proxy reconstruction
Applications behind a CDN or reverse proxy may see an internal hostname, port, or HTTP scheme. Configure a fixed public callback or carefully trust forwarding headers only from known proxies. A global proxy-trust setting can become a security issue when arbitrary clients can supply those headers. Verify canonical-host and HTTPS redirects do not modify the callback path unexpectedly.
Separate environments and app types
Register distinct development, staging, and production callbacks with the correct client registrations. Do not send a localhost callback with production credentials unless the provider explicitly allows it. Native and mobile applications may use claimed HTTPS URLs, custom schemes, or loopback callbacks under provider-specific rules; follow the platform registration rather than copying a web callback pattern.
Keep redirect validation strict
Do not solve the error by adding a broad wildcard or accepting an arbitrary return URL. Loose matching can send authorization codes to attacker-controlled locations. Register the smallest explicit callback set, validate application return destinations separately, and bind the authorization response to the initiating session with state and PKCE where appropriate.
Retest a new authorization flow
After changing registration or configuration, start a completely new flow and inspect the final authorization request. Existing codes remain bound to their original request. Decode the callback parameter locally with the URL Encoder/Decoder.
Frequently Asked Questions
Must redirect URIs match exactly?
Providers commonly require exact registered components.
Can a proxy cause mismatch?
Yes. It may expose an internal host or scheme to the application.
Should callbacks use wildcards?
Avoid broad wildcards; register narrow explicit callbacks.