'Blocked by CORS policy', but Header is present

Question

I created a REST API using Go and fasthttp and a frontend using Vue. Everytime I make an API request, I get the error Access to XMLHttpRequest at 'http://localhost:55555/auth/login' from origin 'http://localhost:8080' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource in my Browser console. The only time I don't get this error, is the /auth/check route. Also I made an OPTIONS-Request to my backend and got all the CORS Headers. I don't get them if I make a POST or GET request, but I don't know why.

Backend:

webRouter := router.New()

auth := webRouter.Group("/auth")
auth.GET("/check", authCheck)
auth.POST("/login", authLogin)
auth.GET("/logout", authCheck)

err = fasthttp.ListenAndServe(":"+port, func (ctx *fasthttp.RequestCtx) {
    ctx.Response.Header.Set("Access-Control-Allow-Origin", "*")
    ctx.Response.Header.Set("Access-Control-Allow-Headers", "authorization, content-type, set-cookie, cookie, server")
    ctx.Response.Header.Set("Access-Control-Allow-Methods", "POST, GET, OPTIONS")
    ctx.Response.Header.Set("Access-Control-Allow-Credentials", "false")
    webRouter.Handler(ctx)
})
if err != nil {
    panic(err)
}

Frontend request:

axios.create({
    baseURL: 'http://localhost:55555'
}).post('/auth/login', {
    email: this.email,
    password: this.password
}).then(response => {
    console.log(response)
}).catch(err => {
    console.log(err)
})

Answer 1

I fixed my issue. I read the docs of fasthttp another time and figured out that the ctx.Error() method clears all headers. Instead I am now setting the response code and error message manually and everything works fine.