API Gateway CORS no Access-Control-Allow-Origin header

Question

Although CORS has been set up through API Gateway and the Access-Control-Allow-Origin header is set  I still receive the following error when attempting to call the API from AJAX within Chrome      XMLHttpRequest cannot load http   XXXXX execute-api us-west-2 amazonaws com beta YYYYY  No  Access-Control-Allow-Origin  header is present on the requested resource  Origin  null  is therefore not allowed access  The response had HTTP status code 403    I attempted to GET the URL through Postman and it shows the above header is successfully passed     And from the OPTIONS reponse     How can I call my API from the browser without reverting to JSON-P

User · Answer

Deploying the code after enabling CORS for both POST and OPTIONS worked for me

User · Answer

In Python you can do it as in the code below      statusCode    200   headers          Content-Type    application json        Access-Control-Allow-Origin                body   json dumps             temperature    tempArray       time   timeArray

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Got my sample working  I just inserted  Access-Control-Allow-Origin        inside headers    in the generated nodejs Lambda function  I made no changes to the Lambda-generated API layer   Here s my NodeJS    use strict   const doc   require  dynamodb-doc    const dynamo   new doc DynamoDB    exports handler     event  context  callback     gt        const done     err  res     gt  callback  null            statusCode  err    400     200           body  err   err message   JSON stringify res           headers    Access-Control-Allow-Origin                       switch  event httpMethod                            Here s my AJAX call    ajax       url   https   x execute-api x-x-x amazonaws com prod fnXx TableName x       type   GET       beforeSend  function         loader    show          success  function  res     alert  JSON stringify res            error function e   alert  Lambda returned error n n    e responseText          complete function        loader   hide

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If you have tried everything regarding this issue to no avail  you ll end up where I did  It turns out  Amazon s existing CORS setup directions work just fine    just make sure you remember to redeploy  The CORS editing wizard  even with all its nice little green checkmarks  does not make live updates to your API  Perhaps obvious  but it stumped me for half a day

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If anyone else is running into this still - I was able to track down the root cause in my application    If you are running API-Gateway with custom Authorizers - API-Gateway will send a 401 or 403 back before it actually hits your server  By default - API-Gateway is NOT configured for CORS when returning 4xx from a custom authorizer   Also - if you happen to be getting a status code of 0 or 1 from a request running through API Gateway  this is probably your issue   To fix - in the API Gateway configuration - go to  Gateway Responses   expand  Default 4XX  and add a CORS configuration header there  i e   Access-Control-Allow-Origin        Make sure to re-deploy your gateway - and voila

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I found a simple solution within   API Gateway   Select your API endpoint   Select the method  in my case it was the POST   Now there is a dropdown ACTIONS   Enable CORS    select it    Now select the dropdown ACTIONS again   Deploy API  re-deploy it     It worked

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I got mine working after I realised that the lambda authoriser was failing and for some unknown reason that was being translated into a CORS error   A simple fix to my authoriser  and some authoriser tests that I should have added in the first place  and it worked   For me the API Gateway action  Enable CORS  was required   This added all the headers and other settings I needed in my API

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In my case  I was simply writing the fetch request URL wrong  On serverless yml  you set cors to true   register-downloadable-client      handler  fetch-downloadable-client-data register register     events        - http            path  register-downloadable-client           method  post           integration  lambda           cors  true           stage    self custom stage    and then on the lambda handler you send the headers  but if you make the fetch request wrong on the frontend  you re not going to get that header on the response and you re going to get this error  So  double check your request URL on the front

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I am running aws-serverless-express  and in my case needed to edit simple-proxy-api yaml    Before CORS was configured to https   example com  I just swapped in my site s name and redeployed via npm run setup  and it updated my existing lambda stack                method response header Access-Control-Allow-Origin    https   example com          proxy    method response header Access-Control-Allow-Origin    https   example com

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In my case  since I was using AWS IAM as the Authorization method for API Gateway  I needed to grant my IAM role permissions to hit the endpoint

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For me  as I was using pretty standard React fetch calls  this could have been fixed using some of the AWS Console and Lambda fixes above  but my Lambda returned the right headers  I was also using Proxy mode  and I needed to package my application up into a SAM Template  so I could not spend my time clicking around the console  I noticed that all of the CORS stuff worked fine UNTIL I put Cognito Auth onto my application  I just basically went very slow doing a SAM package   SAM deploy with more and more configurations until it broke and it broke as soon as I added Auth to my API Gateway  I spent a whole day clicking around wonderful discussions like this one  looking for an easy fix  but then ended up having to actually read about what CORS was doing  I ll save you the reading and give you another easy fix  at least for me   Here is an example of an API Gateway template that finally worked  YAML   Resources    MySearchApi      Type  AWS  Serverless  Api     Properties        StageName   Dev        Cors          AllowMethods   quot  OPTIONS  GET  quot          AllowHeaders   quot  Content-Type X-Amz-Date Authorization X-Api-Key X-Amz-Security-Token  quot          AllowOrigin   quot     quot        Auth          DefaultAuthorizer  MyCognitoSearchAuth         Authorizers            MyCognitoSearchAuth              UserPoolArn   quot  lt my hardcoded user pool ARN gt  quot              AuthType   quot COGNITO USER POOLS quot          AddDefaultAuthorizerToCorsPreflight  False  Note the AddDefaultAuthorizerToCorsPreflight at the bottom  This defaults to True if you DON T have it in your template  as as far as I can tell from my reading  And  when True  it sort of blocks the normal OPTIONS behavior to announce what the Resource supports in terms of Allowed Origins  Once I explicitly added it and set it to False  all of my issues were resolved  The implication is that if you are having this issue and want to diagnose it more completely  you should visit your Resources in API Gateway and check to see if your OPTIONS method contains some form of Authentication  Your GET or POST needs Auth  but if your OPTIONS has Auth enabled on it  then you might find yourself in this situation  If you are clicking around the AWS console  then try removing from OPTIONS  re-deploy  then test  If you are using SAM CLI  then try my fix above

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1  I needed to do the same as  riseres and some other changes This are my response headers   headers                 Access-Control-Allow-Origin                      Access-Control-Allow-Headers   Content-Type X-Amz-Date Authorization X-Api-Key X-Amz-Security-Token                Access-Control-Allow-Credentials    true               Content-Type    application json              2  And  According to this documentation   http   docs aws amazon com apigateway latest developerguide how-to-cors html  When you use proxy for lambda functions on API Gateway config  the post or get methods have no added headers  only the options does  You must do it manually in the response server or lambda response    3  And  Beside that  I needed to disable the  API Key Required  option in my API gateway post method

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I just added headers to my lambda function response and it worked like a charm  exports handler   async  event    gt        const response             statusCode  200          body  JSON stringify  Hey it works            headers    Access-Control-Allow-Origin                     return response

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Another root cause of this problem might be a difference between HTTP 1 1 and HTTP 2   Symptom  Some users  not all of them  reported to get a CORS error when using our Software   Problem  The Access-Control-Allow-Origin header was missing sometimes   Context  We had a Lambda in place  dedicated to handling OPTIONS request and replying with the corresponding CORS headers  such as Access-Control-Allow-Origin matching a whitelisted Origin   Solution  The API Gateway seems to transform all headers to lower-case for HTTP 2 calls  but maintains capitalization for HTTP 1 1  This caused the access to event headers origin to fail   Check if you re having this issue too   Assuming your API is located at https   api example com  and your front-end is at https   www example com  Using CURL  make a request using HTTP 2   curl -v -X OPTIONS -H  Origin  https   www example com  https   api example com   The response output should include the header    lt  Access-Control-Allow-Origin  https   www example com  Repeat the same step using HTTP 1 1  or with a lowercase Origin header    curl -v -X OPTIONS --http1 1 -H  Origin  https   www example com  https   api example com   If the Access-Control-Allow-Origin header is missing  you might want to check case sensitivity when reading the Origin header

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I get the same problem   I have used 10hrs to findout     https   serverless com framework docs providers aws events apigateway      handler js   use strict    module exports hello   function event  context  callback     const response       statusCode  200    headers         Access-Control-Allow-Origin            Required for CORS support to work      Access-Control-Allow-Credentials    true    Required for cookies  authorization headers with HTTPS         body  JSON stringify    message    Hello World          callback null  response

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For Googlers   Here is why    Simple request  or  GET POST with no cookies do not trigger preflight When you configure CORS for a path  API Gateway will only create an OPTIONS method for that path  then send Allow-Origin headers using mock responses when user calls OPTIONS  but GET   POST will not get Allow-Origin automatically If you try to send simple requests with CORS mode on  you will get an error because that response has no Allow-Origin header You may adhere to best practice  simple requests are not meant to send response to user  send authentication cookie along with your requests to make it  not simple  and preflight will trigger Still  you will have to send CORS headers by yourself for the request following OPTIONS   To sum it up    Only harmless OPTIONS will be generated by API Gateway automatically OPTIONS are only used by browser as a precautious measure to check possibility of CORS on a path Whether CORS is accepted depend on the actual method e g  GET   POST You have to manually send appropriate headers in your response

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In addition to others comments  something to look out for is the status returned from your underlying integration and if the Access-Control-Allow-Origin header is returned for that status   Doing the  Enable CORS  thing only sets up 200 status  If you have others on the endpoint  e g 4xx and 5xx  you need to add the header yourself

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After Change your Function or Code Follow these two steps   First Enable CORS Then Deploy API every time

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For me  the answer that FINALLY WORKED  was the comment from James Shapiro from Alex R s answer  second most upvoted     I got into this API Gateway problem in the first place  by trying to get a static webpage hosted in S3 to use lambda to process the contact-us page and send an email   Simply checking     Default 4XX fixed the error message

[ajax] API Gateway CORS: no 'Access-Control-Allow-Origin' header

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