CrytoHelpers.ts

export default class CrytoHelpers {
	static generateRandomString(): string {
		var array = new Uint32Array(64);
		window.crypto.getRandomValues(array);
		return Array.from(array, dec => ('0' + dec.toString(16)).substr(-2)).join('');
	}

	static async pkceChallengeFromVerifierAsync(v: string): Promise<string> {
		const hashed = await this.sha256(v);
		return this.base64urlencode(hashed);
	}

	private static async sha256(plain: string): Promise<ArrayBuffer> {
		const encoder = new TextEncoder();
		const data = encoder.encode(plain);
		return await window.crypto.subtle.digest('SHA-256', data);
	}

	// Base64-urlencodes the input string
	private static base64urlencode(str: ArrayBuffer): string {
		// Convert the ArrayBuffer to string using Uint8 array to convert to what btoa accepts.
		// btoa accepts chars only within ascii 0-255 and base64 encodes them.
		// Then convert the base64 encoded to base64url encoded
		//   (replace + with -, replace / with _, trim trailing =)
		return btoa(String.fromCharCode.apply(null, new Uint8Array(str)))
			.replace(/\+/g, '-')
			.replace(/\//g, '_')
			.replace(/=+$/, '');
	}
}

OAuthService.ts

async refreshAccessTokenAsync(): Promise<TokenResponse> {
		const refreshToken = localStorage.getItem(Conventions.refreshTokenKey);
		if (!refreshToken) {
			throw new Error(`No refresh token found in local storage key '${Conventions.refreshTokenKey}'.`);
		}

		const tokenRequest: TokenRequest = {
			refreshToken: refreshToken,
			grantType: 'refresh_token', // TODO: Make enum
			clientId: this.clientId
		};

		const url = `${this.wemogyIdentityPublicUrl}/oauth/token`;
		const response = await this.httpClient.post<TokenResponse>(url, tokenRequest);
		const tokenResponse = Object.setPrototypeOf(response.data, new TokenResponse()) as TokenResponse;

		const now = new Date();
		now.setSeconds(now.getSeconds() + tokenResponse.expiresIn);
		localStorage.setItem(Conventions.accessTokenKey, tokenResponse.accessToken);
		localStorage.setItem(Conventions.idTokenKey, tokenResponse.idToken);
		localStorage.setItem(Conventions.refreshTokenKey, tokenResponse.refreshToken);
		localStorage.setItem(Conventions.expiresAtKey, now.getTime().toString());

		return tokenResponse;
	}