A signing provider function written in typesript

provideSign.ts

/**
 * A reusable signing function using the token passed to a provider
 * 
 * @param data data to sign
 * @returns Base64 signature
 */
export type TokenSign = (data: string) => Promise<string>;

/*
* Constants for signing
*/
export const SIGNING: {
    MIN_TOKEN_LENGTH: number,
    ALGORITHM: AlgorithmIdentifier | RsaPssParams | EcdsaParams
} = {
    MIN_TOKEN_LENGTH: 24,
    ALGORITHM: { name: 'HMAC', hash: 'SHA-512' }
};

import { SIGNING } from "./SIGNING";
import { TokenSign } from "./TokenSign";

/**
 * provides a signing function using the token passed
 *
 * @param token token to use for signing
 * @returns a signing function
 */
export function provideSign(
    token: string,
    algorithm: AlgorithmIdentifier | RsaPssParams | EcdsaParams = SIGNING.ALGORITHM
): TokenSign {

    if (token == null
        || typeof token !== 'string'
        || token.trim().length < SIGNING.MIN_TOKEN_LENGTH)
        throw new Error(`Token for signing must be at least ${SIGNING.MIN_TOKEN_LENGTH} characters long`);

    const encoder = new TextEncoder();

    const getKey = crypto.subtle
        .importKey(
            'raw',
            encoder.encode(token),
            algorithm,
            false,
            ['sign']
        );

    return async data => {
        if (data == null
            || typeof data !== 'string'
            || data.trim().length === 0)
            throw new Error('Data to sign must be provided');

        const signature = await crypto.subtle
            .sign(
                algorithm,
                await getKey,
                encoder.encode(data)
            );

        return btoa(String.fromCharCode(...new Uint8Array(signature)));
    };
}