How to parse map[string]interface{} passed in context

Problem

I wish to add variable to the request context in a Middleware

fmt.Println(variable) // => map[key1:some text key2:[str1] key3:1234567890]

Then, access value.keyx in my Route handler

v := variable[key1]
fmt.Prinln(v) // => some text

// AnotherFunction requires a `string`
AnotherFunction(v)

Middleware

I add this variable to a context in a middleware such as:

// Middleware function
...
fmt.Println(variable) // => map[key1:some text key2:[str1] key3:1234567890]
fmt.Println(variable["key1"]) // => some text
ctx := context.WithValue(r.Context(), "var", variable)

which works fine.

Route Handler

Then, in my route handler I am able to access the context by doing

values := r.Context().Value("var")

fmt.Println(values) // => map[key1:some text key2:[str1] key3:1234567890]
fmt.Println(reflect.TypeOf(values)) // => map[string]interface {}

The issue is when I try to access the properties inside values

Attempts

1. I tried the same I did in Middleware

fmt.Println(values["key1"]) // => invalid operation: cannot index claims (variable of type interface{})

2. I investigated this solution but value is not a JSON object

3. Doing a cast I am able to access "key1". BUT, it is not accepted by AnotherFunction(s string) which requires a string.

values := r.Context().Value("var")
casted := values.(map[string]interface{})

keyValue := casted["key1"]

fmt.Println(keyValue) // => some text
fmt.Println(reflect.TypeOf(keyValue)) // => string

// AnotherFunction requires a string input
AnotherFunction(keyValue) // => cannot use keyValue (variable of type interface{}) as string value in argument to AnotherFunction

So, I do another cast to work

values := r.Context().Value("var")
casted := values.(map[string]interface{})

keyValue := casted["key1"].(string) // <= Another cast

fmt.Println(keyValue) // => some text
fmt.Println(reflect.TypeOf(keyValue)) // => string

// AnotherFunction requires a string input
AnotherFunction(keyValue) // => OK

I'm convinced that there's another more correct way to do it.